Dodgy old boiler

by Nick  

So, yesterday, we woke up thinking, 'gosh, it's a bit fresh this morning'. Then, when we went into the bathroom, and felt the chill, and heard the clicking sounds, we realised our boiler wasn't working. It's a Potterton Profile 50e which we inherited with the house. When we did our kitchen/bathroom extension, we had it moved into a new airing cupboard, where it looks like this:

What an old boiler

The problem on this particular day was that the main gas burner wouldn't light. It has an internal fan which would spin for about three seconds, then click to a stop. Then spin up again. And stop. And so it repeated, without igniting.

We had to go to the shops yesterday, and when we came back, it had come back to life, so we thought 'phew' and didn't worry so much. Then this morning, it didn't come back to life. We had exactly the same symptoms about 3-4 years ago, when the boiler last stopped working. We paid about £120 to have it repaired then, so weren't delighted to have it happen again.

I took a look at the troubleshooting chart in the installation guide and it pointed towards the gas valve as the culprit, but that looked fairly new, and it seemed unlikely to stop and start again, so I wasn't convinced by that. Then I realised that the chart presumed that you were starting from scratch. Yet the pilot light was already lit on ours. I extinguished the pilot, and tried to relight. This time, nothing. Just the fan cycling. The pilot light stayed out. Based on this, the chart said to replace the electronic control board (a 407677 PCB apparently). This wasn't good news. Even on eBay, they cost over £100.

Given this was the second time our boiler had broken down, we were beginning to wonder whether we should bite the bullet and fit a new condensing boiler (something like a nice Worcester-Bosch Greenstar). The downside would be having to stump up anything from £1,500 to £3,000 depending on labour costs. And quick. Gulp. XX(

Feeling rather glum, I did a bit more optimistic googling, and found a couple of interesting articles. One described the same problem exactly, and confirmed the PCB as the problem. Then I noticed lots more articles on which mentioned similar problems with Potterton circuit boards. The phrase design flaw comes to mind...

One of these articles struck gold. Again it described the problem, but this time one of the respondents had stripped down his control board, and concluded that the most likely way for it to fail is with three electrolytic capacitors. The thing with electrolytic capacitors is that they contain electrolyte - a liquid - which slowly evaporates until they fail. Normally this is a slow process (many years), but of course, if you heat a liquid it evaporates quicker. It's lucky that boilers are so cold, isn't it? Oh, wait...

Here's the nub of the article I found. You replace the three capacitors, and see what happens. I did it. It cost me 83p plus the petrol to go to Maplin on a Sunday. Tony Taunton, I salute you. If you're reading this (especially because you googled something like 'Potterton Profile fan problem', or fan cycles, won't light, doesn't ignite etc), I'll describe what I did as a list, with a few pictures, and quote the relevant bit of Tony's original post for the detail. Apparently it's the same circuit board in a Potterton Prima too, so this maybe relevant if you have one of those.

Obviously, this is only a job for the competent user of a soldering iron, who understands what 240V mains electricity can do. I don't encourage anyone to do this. All information published on this site is used entirely at the site visitor or user's risk. No warranties are expressed or implied. Do not DIY with gas. It can kill you and others, and incompetent works can invalidate home insurance.

  1. Turn off the electricity supply to the boiler before you start. Remove the cover at the bottom (it slides forward - you may need to remove a screw from the base first):

    Cover off

  2. Just below the main thermostat at the front is a screw, which you undo to release the bottom panel to access the electrics.


  3. The 407677 control board is the pcb with a black cover towards the back. Detach the two block connectors at the front. This leaves five wires at the front left which you need to loosen at their far ends.
  4. Unclip the green and yellow earth lead, and remove the blue neutral lead from its terminal after unscrewing.
  5. Unclip the brown lead from the back of the overheat sensor, and the two white leads from the back of the main thermostat (don't worry about which way round those two go). Top tip: take a couple of digital photos as you go to remind you where to reconnect later, if you're not sure.
  6. Finally, gently release the white electrode wire, sideways from the back left of the board - unlike the others it looks like it's soldered, but it is a friction fit.
  7. Now you can ease the whole board off its four plastic mounts. You'll probably need to squeeze the top of each post with some narrow-nosed pliers.
  8. After wiping off the grime, this was mine:
    407677 of doom
  9. Lift off the black cover (you may need to cut off any glue on the underside), and you'll see this:

    Oh no, I've invalidated my warranty.

    I've circled the three capacitors which I replaced. Tony wrote:

    The electrolytic capacitors have a "+" marked on the board, and you must observe this. C4 and C7 were 22uF at 63v and C6 was 4.7 at 63v (but check on your board) The 63v is important - don't get any lower voltage. Get high temperature (105deg) if you can, as they get hot, and that's what shortens their life.

    Use as fine-tipped and hot a soldering iron as you can, to minimise heating of the components themselves. Whip out the old ones, and put in shiny new ones.

  10. While I was at it, I freshened up some of the other solder joints. Probably not necessary, but I figured I may as well.
  11. Reassembly is, as they say, the reverse of disassembly.

So, with that, I powered up, turned on the hot water 'stat, turned up the boiler thermostat and after a few seconds, I had warm, blue, burny goodness, and my bank account karma was much improved.

So, this is a public record of how I saved myself some money. Remember that I checked the official Potterton troubleshooting guide first to convince myself that this was the cause of my boiler failure. Please don't explode your house trying to do this. Bear in mind that a faulty repair could invalidate your home insurance. Landlords and employers are legally obliged to use a registered CH engineer for all gas work. If it doesn't work for you, please don't ask me to buy you a new control board. Instead, blame the stupid design which put heat-sensitive components next to a very hot place, and consider it a couple of quid worth a punt.

On the other hand, if you do try this and it works, I'd love you to comment to let me know that it helped. There should be a link nearby. Comments are now closed. Thanks to all who contributed.

After about 6 weeks I'm delighted this has already saved hundreds of pounds for people. If you have a blog, please mention this link to spread the word! If it's saved you the cost of a replacement boiler and you'd like to express your thanks with a donation (secured by PayPal) to support my hosting costs, it'd be very welcome. I'll donate 50% of your contributions to National Energy Action, the UK's leading fuel poverty charity, campaigning for warmer homes - it seems like an appropriate cause.

Edit 11/11/2008: Steve found a completely different PCB with the same number. He took a photo which I'm posting with his kind permission in case it's useful to others. As usual, click to enlarge:

Potterton PCB

Edit 1/3/2009: John B fixed his Potterton Netaheat boiler suffering similar symptoms. His boiler has a 407676 PCB, and he's kindly let me post some pictures of this circuit board, as well as give details of the Maplin part numbers required. I've posted that separately here.

Edit 22/5/2009: Registered gas engineer Chris points out that faulty gas works, if causing an accident, may mean that your home insurance would not pay out. I agree. Do not DIY with gas. That's what Gas Safe registered engineers are for (note that CORGI registration is not a legal indicator of competence since 1 April 2009). I don't believe that repairing a removable PCB constitutes gas works under the Gas Regulations, but you may think differently, in which case, just call a professional.

Edit 6/6/2010: Over 15,000 views for this page. Wow! Thanks again for all the valuable comments and contributions.

Edit 19/6/2011: Over 26,500 views and over 200 comments. Honestly not what I expected. I'm closing comments today, as this post is three years old now, and most new comments ask for advice with specific problems. I can't give advice, as I'm not qualified to do so. As I've done above and in the comments below, I suggest you look at the troubleshooting chart in the installation guide to help identify the fault. If it's not the fault I had, please consult a Gas Safe professional. If it is the same fault, then your action is up to you. Stay safe, and may you be warm.


Comment from: Greg  

Dear Nick I had the same symptoms in my one ( profile 30).My story started in last week when I’ve notice that something is not right.On Friday I had engineer visiting me .But that guy had no clue, he replaced air pressure switch and nothing happened.I could see in his eyes how he loses hope.So we both sad goodbye.The only difference was That temperature in my house was about 15 C and boiler still not fixed.I was loosing any hope and than about 2AM I found your website I start reading."Of course” I said Nick is right. so today I went to Maplins I’ve spend whole 49p and I’ve save £375(pcb cost described by engineer) or £1900 for new boiler (as he recommended) I want say thank you very much that you showed me “light in the tunnel ” Potterton works like never before.Once again thanks

16/02/08 @ 21:24
Comment from: Clivey

I too had similar intermittent problems with our Profile 50e.

After a lot of investigation (watching the PCB whilst the bolier was operating with the room lights out) I found that one end of the Zener diode - Z3 on the board - was arcing as it had unsoldered itself from the board. After pulling the board and soldering a new zener (50 pence from Maplin) the bolier worked fine. It all seems to point to a poorly designed and manufactured PCB.

Replacement PCBs cost up to £180 and you would expect to pay for an hours labour for fitting plus VAT for Mr Darling.

I’m surprised Potterton don’t get them made in China as they’d probably be better made!

11/03/08 @ 23:30
Comment from:

@Clivey, thanks, good tip!

12/03/08 @ 21:46
Chris Fitzpatrick

Fantastic post Nick. Exactly the kind of thing the internet should be used for and often isn’t sadly. Followed your steps to the letter as had the same old cycling fan symptoms and didn’t fancy buying another pcb that only seem to last approx 4 yrs and thanks to your post, now have a Potteron profile boiler working 100% once more for the total outlay of 78pence! Like you also found a dry joint which I soldered up.
Many thanks,

27/03/08 @ 13:34
Comment from:

Hi Chris, Thanks for the feedback; glad to hear it’s helped someone else. I’m beginning to wonder if I should start Pottertonics Anonymous. There’s obviously a lot of sufferers out there!

27/03/08 @ 21:01
Comment from: mike

After checking diagnostic chart,replace electronic control 407677 was called for.About to spend £130.00,found your page,thought, what have i to loose? off to Maplin,35p poorer,outcome,happy boiler,happy mike,thank you very much.

30/03/08 @ 12:37
Comment from: Peter  

Thanks for such a good site. As has been said previously this is what the internet should be all about.
I have a dead 407677 in front of me , with what looks like a burnt R15 which sits next to relay RL2.
I would very much appreciate it if you could tell me what its value should be in ohms.
I will also check all electrolytics and check for dry joints.
Many thanks

07/04/08 @ 15:44
Comment from:

Hi Peter,

I hope you won’t mind that I won’t disassemble my working boiler to check for sure! I’ve looked back at the digital photos I took, and it looks like R15 is brown-black-yellow, which would make it 100K. I wouldn’t swear to it though, as the flash photo might affect how the colour looks.

Bear in mind too that if something’s burnt, it might be a symptom of multiple component failure, in which case you may find it easier to go for a board exchange from ebay. From what I read, for instance, the relays aren’t so easy to source…

Let me know how it goes, don’t blow your house up, and good luck!

07/04/08 @ 20:12
Comment from: Andrew Bourne
Andrew Bourne

Your posts have been very helpful Nick. Thanks to you and the other comments here, I’ve sorted my boiler too!

It is a Prima 60F but has exactly the same board. For many months now it used to stop working (no flame visible) but the pump and fan were still on. Sometimes a bit of a slap against the boiler kicked it back into life!

The PCB is mounted on a drop-down tray underneath the boiler. In this hang-down position it seemed to work for quite a while, but that didn’t last long (a few weeks and it all started playing up again). Sometimes it would work - other times it wouldn’t. Then I noticed one day that there was some arcing on the PCB on the connector that lead to the gas solenoids.

Once I plucked up the courage to remove the board (it’s in a very difficult position), I noticed that there was a very bad dry joint on the connector. The zener diode also looked like it had become very hot due to the scorching on the PCB. Anyway, soldering up the bad joint and any other ‘iffy’ looking joints seems to have cured the problem.

The capacitors and other components looked OK so I haven’t changed them yet - I will if it packs up again.
My advice is to carefully check the solder joints on the bottom of the board and freshen them up as you mentioned Nick.

Something that may help others is how to remove the electrode lead on the back of the PCB (the white lead that connects to the pilot and electrode assembly). It is a spade connector that (with some care) pulls straight away from the board (it is not soldered as I first thought).

A useful web site I found has all the installation instructions and parts details for most boilers:

09/04/08 @ 14:28
Comment from:

Andrew, thanks for the useful contribution. You’re right about the spark connector on the back-left edge. I remember when I looked at it I thought it was soldered, as it didn’t have a connector like the rest. I’ll edit the main post to make that clearer.

09/04/08 @ 20:32
Comment from: Andrew96

if anyone has a burnt relay then they are still available from part number 492-6754 and cost £1.14 each, plus p/p and vat in the uk
for that cost might be worth keping 2 as a spare just in case!

19/04/08 @ 13:30
Comment from: Andrew96

R15 is indeed 100K, it seems there not actually burnt out just suffer with getting warm! its only a 0.25watt resistor so replacing it with a 0.5w one should stop the discolouration and also will stop it failing in the future, only a few pence to do and could well be worth doing at the same time as other bits

19/04/08 @ 13:36
Comment from:

Hi Andrew, thanks for the additional feedback. I’m sure it’ll be useful to others!

20/04/08 @ 10:53
Comment from: Peter

Hi ,
On 7th April I indicated that on the pcb of 47677 resistor R15 was burnt.Thanks for telling me it was 100K. looking closely at the resistor it has been running hot but not burnt out.Infact both ends were floating .They looked soldered but there was a complete ring maybe 0.1mm of space .The resitor wire was soldered to the centre of the pcb pad but was floating from the associated tracks.I replaced the 0.25W resistor with 100K vishay PR02 ( 2w but in a small profile )taking the wires to the local pins of the connector ,following the pcb track.Checked the electrolytics still had capacitance and resoldered 1.5W zenner connections just for good measure.Board now works OK. Thanks for such a good site which also allows for great 2way comms.

24/04/08 @ 17:22
Comment from:


Not really, I’m afraid. I’m no CH engineer, so what I’ve gleaned is only from my own limited experience. It isn’t clear from your comment if the fan is cycling, or running continuously. Can you clarify?

Peter, glad to have helped. I remember my better half complaining at the time how long I was taking to write the original post! Nice to know it was worth it.

25/04/08 @ 12:58
Comment from: nigel

Just a short note to say how useful your cure for the dodgy electronics on the potterton profile range of boliers was. I was having the stop start symptons that seemed to fit your description and wasn’t prepared to call in a plumber (cause I’m a tight fisted northerner!) and decided that your suggestions were worth a try and certainly wouldn’t do any harm! I ordered the components specified and followed your guidance. The only problems encountered were getting the pcb out, without disturbing any thing else, quite fiddly! Also when I ordered the capacitors I didn’t realise that two are radial and one is axial, I got all radial, as it turned out there is space to fit either, the component is the same apart from the physical shape. Soldered all the components in ( when removing the old ones you have to be careful not to take part of the circuit track with it, as I did in my haste!) Put everything back as was and fired it up….BINGO! Problem sorted, all for the princly some of £3.24 inc. postage (I bought a few spares just in case!)
Thankyou again for the remedy, I was initially sceptical and I am not one for electronics, but I am a great believer in repair if at all possible!

02/05/08 @ 12:02
Comment from: Andrew96

the sequence is… fan starts, if fan runs corectly then the pressure switch operates, this turns on the pilot gas valve and spark generator, once pilot is lit the pcb senses this and turnes on the main gas valve……
Iif the fan is running and nothing else is hapening it is likely there is a problem with the pressure switch or the tubes that sense the pressure.

If the spark is hapening but there is no gas the gas valve is suspect, i have a prima 80 and this has a ’sit830′ gas valve that seems more prone to this than the honeywell one, but saying that i have had honeywell coils go open circuit too! if the gas valve is suspect you will need a corgi engineer to replace it

it sounds like you have the pressure switch problem, check the silicone pipes in case they are loose and make sure the entrances into the pipes are not blocked or partially blocked, you can if your really carefull LIGHTLY blow into the red tube and hear the switch operate, but if you have no knowlege of electrics then best leave diagnosis to a corgi person as well

good luck

30/05/08 @ 23:51
Comment from: Andrew96

the 100k resistor is actually across the main gas valve so it has 230V across it all the time the valve is on, as far as i can see it is either to disipate any residue voltage across the gas valve coil so to turn it off quicker when the moment the 230v disapears, or it is to kill any high voltage spike across the coil when the voltage drops ie boiler turns the gas off, either way it apears not to critical and as far as i can see it is not a component that will stop the boiler operating

I replaced it with a higher wattage one,the one fitted is a 0.25w one, more than adiquate when you work out the current through it but as we have seen it does tend to blacken, so i suggest a 0.5w resistor as this will handle it better, it will fit fine and is no problem to be a uprated wattage, also will stop it blackening in the future
hope this helps

30/05/08 @ 23:58
Comment from: mark  

hi dr-nick
i have a potterton profile and i woke this morning to no hot water, checked the boiler no pilot light, i turned it off and on again nothing no pilot no fan nothing, timer is on i assume there is power does this sound like the pcb problem you had?
cheers mark

23/07/08 @ 17:16
Comment from:

Hi Mark,

If the fan is completely silent then it’s probably not the PCB. The typical way that Profile PCBs fail is that you’ll hear a cyclical clicking as the gas valve opens, followed by the fan whirring quietly for a few seconds before shutting off and the whole thing repeating.

If you don’t hear the fan at all, then check the mains fuse which powers the boiler (although the timer probably works off this), and also the overheat sensor (a little plastic pushswitch which pops out downwards through a hole in the bottom of the boiler if it’s got too hot). If it’s neither of those, then it usually points to a failed fan or air pressure switch which probably means a CORGI visit I’m afraid.

Best of luck with it, and let me know how you get on.

23/07/08 @ 22:45
Comment from: Tim

I’m having the same problems as described and have removed the 407677 board. Looking at all the above comments it seems worth replacing all of C4, C6, C7, R15, Z3 as none of these is very expensive, and I don’t want to have to take the board out again.

I have found suitable replacements for all but Z3 on the Maplin website. Reading what I can see without unsoldering Z3 from the board it says “W03C51″.

Does anyone know the correct spec for this component, and ideally the Maplin part number?


15/08/08 @ 19:50
Comment from: Mick

Hi Nick

My Potterton has had these symptons on and off for the last couple of years, I’ve tended to ignore it as it eventually used to light. Friday probably was the final breakdown as it continued to poll without lighting, prompting me to look on the web. Am I glad I found your excellent site. Initially just tried resloldering all joints as everything looked perfect, unfortunately it did not resolve my problem, back out with the PCB and changed the said capacitors, 65p from Maplins. Put the board back in, and fired up first time. Many thanks

30/08/08 @ 16:34
Comment from: AJ

Can anyone help with some advice please?
I have a profile prima80 and for the first time ever during an annual service the guy (new this year to us) ran a naked light from a cigarette lighter up the joint on the white cabinet and when it reached the very top th flame ducked down towards the joint and he then declared that we couldnt use it until he fitted a new seal and it may be likely that we need a new boiler. I have been caught so often in the past I am just wondering if this could actually be true. I thought this boiler was room sealed and that the flue pipe provides the air in and exhaust out and that the case was just cosmetic. Anyone know please???

09/09/08 @ 19:53
Comment from:

Alan reports back useful (if conflicting) results from

“You certainly won’t NEED a new boiler, but you will probably need a new case seal…they compress. If it is a negative pressure boiler ie sucking in the flame, it won’t do any harm for a day or so. There is a manufacturer tolerance in the seal that allows some movement of the flame. It should be done by a match by the way, a lighter flame is propelled.”

“hi this model boiler is a positive case and he is correct, I normally test it with a smoke match you can only use a seal that’s made by the manufactures if its still available, the reason he has told you that you cannot use it is because fumes are entering the room, so its classed as I D”

“pretty sure the prima is negative pressure, the profile is positive, maybe where your getting confused. In any case if the case seals and grommets are complete and in good condition the manufacturers have an ‘allowable tolerance.’ What that actually equates to is anyone’s guess though but all in all you are allowed a very minor escape, which if required can be corrected with silicone(something I’ve managed to avoid so far)”

10/09/08 @ 21:19

Dr Nick,

many thanks for your beautifully illustrated how-to as well as to the contributors at My Profile 80 has been doing the stop-start thing for a while now and I thought I’d try and sort it before the winter arrives. I bought all three capacitors from Maplin in preparation, but thought I’d start by replacing just C7 (the axial) and then testing the unit out. This did the trick so I thought I’d quit while I was ahead, as my soldering skills are not exactly great. I’ll keep the others handy in case of future problems. Free beer available if you’re ever passing Guildford!


16/09/08 @ 22:28
John Barber

Hello I want to thank you so much ,when i read your account and found I had the same symptoms with my boiler. I was lucky i got a 407677 PCB on ebay for 40 pounds and had already brought it when i read this but your pictures gave me the push i needed to have a go and guess what i changed the PCB and right on the button it started up. My wife was over the moon. I am going to fix the other PCB by changing the electrolytic capacitors thanks again for taking the time to write this articale ,the power of the internet thanks mate.

31/10/08 @ 21:10
Comment from:

Hi John,

Glad it’s worked out for you, especially given the weather we’ve been having lately!

It’s always good to get the comments - it took the best part of a couple of hours to write the original post, but the response over the months has really made it worthwhile.


31/10/08 @ 22:27
Comment from: Jason

Hi, excellent article guys as this matches my predicament with my profile 50e too! Although I have purchased a replacement pcb (sub£60 approx. now) although it states as new I have my suspicions that it may be recon?, but at least I’ll have a spare now and know what to do with it should it fail!

06/11/08 @ 20:56
Comment from: Steve  

Hi Nick
I am right in the middle of dealing with a problem to those outlined above, only that I have a variation on the theme in that my 407677 has a completely different internal layout from the one shown in your illustration. I have pic I can let you have have although as I am not a member I don’t think I can upload it with this post. The only electrolytic caps I can see on my board are C2, C6 & C7.
C2 & C7 are 100uf at 50v@85deg and C6 is a 22uf at 50V@105deg.
Which makes it quite a bit different from the 407677 in your pic.
I have just taken them off the board and it is Sunday night I have not been able to take it any further.

Chances are this may not be read until I have obtained the replacements (heh-heh wishful thinking, most times I need something like this, they have just sold the last one!) and who knows, it might work. (tempting fate again)

My symptons were erratic in that sometimes the fan would cycle and no more would happen, occassionally the unit would do nothing at all and once or twice it lit fully, ran for say 2 mins then refused to relight. All of which has pointed me to the ECU rather than any one single component such as the air-pressure switch which would, as I see it just cause the same train of events each time heat was demanded.

Does anyone have any thoughts, and do you know when the Prima was first sold, as far as I can make out mine was installed in ‘95, long before I bought the house.

May I thank you far a very helpful website.


09/11/08 @ 22:54
Comment from:

Hi Steve,

First I’ve heard of a different layout, but that’s certainly not to discount it! I’d agree with you that the symptoms fit a failing PCB. If so, the first and cheapest candidate is to replace the electrolytic caps, and secondly check for dry joints. As you point out, two of the caps are rated at 85C, which is not that big a number, especially if the boiler is run for years, or in a confined space. As far as age is concerned, we guesstimate ours was mid-90s too.

Do post back if/when you’ve had a go - it’d be good to add to the collective knowledge either way.

Best, Nick

10/11/08 @ 17:17
Comment from: Steve

Hi Nick
Here’s a progress?!? update.

Replaced the electrolytic caps this morning and reconnected the board.

Zilch! Thought- oh no it must be one of the relays - not really enough time to get my head around the problem so decided to acquire refurb board - Based in Watford, collected in person. Helpful people who new about the two different board types. Connected new board - still zilch! Removed main cover to start examining fan and airflow pipework. Boiler was still connected - bad practice I know but in this case good because I touched one of the connectors to the cables that feed the fan. There is a very naff little spade terminal block fixed through a hole in the top right of the case underneath the cover. On doing this I noticed that the fan made a couple of revolutions. To make a short story shorter, it transpired that the naff terminal block had not withstood the heat/time test: It had partially dis-integrated, and the terminals had agreed to separate but were still in touching distance, call it a farewell kiss! I have reconnected the terminals and all appears to be working; at least for the moment.

So in my case I would have been better off invesitgating, thinking things thru and testing with a meter (that there were volts present at the fan feed etc) before jumping to the conclusion that it was the ECU at fault.


11/11/08 @ 19:10
Comment from:

I’ve edited the original post to add Steve’s photo. Useful tip about the fan terminals - I’ve not heard of that before, and a wise point that amateur diagnosis is just that!

Thinking on it, the thing that seems to be consistent with the caps failing is that the fan does cycle reliably every time. Worth bearing in mind!

Thanks again Steve.

11/11/08 @ 19:45
Comment from: Grateful

Thanks a million for this.

14/11/08 @ 13:15
Comment from: Graham Brooke
Graham Brooke

I thought I would check the capacitrors listed and found the main one was C7 the ESR was very low on this whereas the other two weren’t bad.
Thanks very much for the help everyone… its nice to be warm again.

21/11/08 @ 10:48
Comment from: Iain

I was struggling with unreliable firing on my F60 when I came across this web site; MUCH more helpful than anything you will find frequented by gas fitters. Narrowed my issues down to the PCB and discovered 3 dry joints on what is a rather flimsy board that supplied the main gas valve solenoid. A quick bit of soldering and all appears well.
Anybody with fan problems - just check that you can easily spin the fan, the bearings tend to get sticky as the years go by and may need cleaning up.
A quick trip to Maplins is in order so I am ready for the next problem.
Thanks for running this extremely helpful blog.

26/11/08 @ 22:08
Comment from: Paul

Hi Everyone,
I’ve a 50e which was exhibiting the same symptoms - could hear the fan, it would click, and sound of the fan starting up but not get going fully, it wouldn’t ignite, the fan stopped, and the cycle repeated, then after an hour it would finally start up properly. Reset the timer yesterday to compensate (the memsahib hates cold in the morning, oh and the afternoon, and especially at night), and low and behold it wouldn’t start up at all this morning, just the sound of the fan.

So popped out and got a recon pcb 407677 and fitted it, turned on the power, and …… ziltch, nada, nothing.

Any ideas what I should check?

03/12/08 @ 15:06
Comment from:


It’s not clear from your comment whether it’s still doing the same thing with the new PCB, or if it’s now completely dead?

Either way, I think you’re probably wise to look at the fault-finding chart. It seems that Potterton have taken it off their site since I posted the original article, but you can find it on the Internet Archive.

Grab it while you can, and look at p32. If you make progress and have useful feedback, please come back and post again for others. Good luck! Nick

03/12/08 @ 19:52
Comment from: Paul

Thanks Nick,

Sorry if it wasn’t clear, no nothing at all happens now. No fan no clicks just the sound of silence.

So I took out the pcb sprayed the contacts with detoxit (contact cleaning solution) replaced the pcb, and still nothing.

I’ll take the pcb back to where I got it and see if I can get another I was told there is a year warranty.

Thanks for the fault finding chart - I tried to get it a couple of days ago, but as you say Potterton had removed it. I’ll check it out tomorrow too.

Will keep in touch.

PS I thought I’d better say that I’ve also posted on under “Blue nose Paul” to widen the potental expert base. Hope that doesn’t offend anyone!

03/12/08 @ 21:25
Comment from: Paul

The final chapter….

I rang a help line (which shall remain anonymous) and explained my situation and the rather nice chap at the other end of the phone went through what the readings should be for the various connections on the pcb. When I gave him the reading for the fan connections he said the fan was kaput. I took it to the recon establishment who were really helpful, put it on a test rig and said well while the bearings were a bit naff, you won’t get any more speed and therefore air flow out of a new or recon one. Go away and refit the old one, but check the APS, ‘cos that’s my bet on where the problem is.

So I did what I was told and refitted the fan, but I am getting a bit desperate, ‘cos it’s coming to the end of the third day without central heating. Checked the APS and it was clicking fine - oh a useful tip from the recon people was that there may be a pin hole in the diaphragm, to gently blow across or down the tube, get the faint click of the APS actuating, then stick your tongue over the tube to hold the pressure for at least ten seconds. If it clicks while your tongue is over the end of the tube there is a pin hole in the diaphragm, but if it clicks after you take you tongue off the tube then the diaphragm is ok. As I said the APS tested ok.

I am very lucky in that my son who is away at college has two mates who are plumbers. Now why didn’t he get them to do this in the first place you may say.. Well I’m a stubborn old s** and try to work things out myself, but when I’m beat I give up so I called them.

They popped round at 6.00pm tonight and at 6.05 the heating was back on.

When I removed or refitted the pcb I had pushed one of the temperature control spade connectors almost but not quite off the contact, so a glance at it looked ok but it wasn’t connected. A good look at it would have solved the problem. Mind you they had to contort and twist themselves a lot to get a view because of the boiler position, but that’s no excuse I’m sorry to say I missed a loose connection.

Thanks to everyone who commented and I hope that this is a salutary lesson. Check all the contacts are properly made or you may be wondering around for days going nowhere like I did.

And that’s the story and tomorrow we should have heat and morning glory.

04/12/08 @ 23:26
Comment from: Dabs  

Fantastic post. I’ve got a potterton Profile 80e that has had the classic fan cycling problem for ages, I never even knew it was a problem until recently. Anyway, I got the capacitors from Maplins to replace on the PCB and before I could do it the whole thing just packed up. The Mrs obviously unable to survive in anything less than 2000 degrees C started the old ear ache routine so I ended up changing the whole PCB 407677.
What happens now is the boiler fires up first time on CH or DHW demand, runs for about 1 minute and then cuts out, I’m assuming it is overheating. If it does overheat do I have to reset the switch or will it start working again after cooling off for a while? And if it does start working after a while without pressing the reset switch does this mean its not a overheating problem? (Also the reset switch is so flimsey that pressing it doesn’t seem to do anything, should I hear it click or something?). The pump has power and I can hear it spinning so seems to be working ok so not sure what the problem is. Maybe blockage somewhere else but don’t know how to check. Can you help?

05/12/08 @ 00:52
Comment from:

@Paul, sometimes it’s the simplest of things. Thanks for the troubleshooting tips!

@Dabs, I think you’re best looking at the fault-finding guide. From a (very!) amateur perspective it sounds like either a thermostat failing, or a circulation problem.

See how far the main flow pipe warms up before it cuts out. You should feel warmth more than 50cm away quite quickly if circulation is ok. If the overheat stat has tripped, then you do have to push the reset switch manually - it doesn’t reset itself. I can’t recall if it gives a positive click or not, but I seem to recall the switch pops out further than normal.

Oh yes, speaking of the simplest things - you have turned the main ’stat up from minimum haven’t you? Let me know how it goes. Nick

05/12/08 @ 07:51
Comment from: Chris  

Dear Nick,
Have read through all the posts & hope you may have some ideas - I have a Potterton Prima 60f, the boiler fires up OK on demand & runs for around 15 minutes until it heats up.
It then starts to switch on and off at very short intervals ( say off for 3 or 4 minutes then a 1 to 1.5 minute burn).
I had the unit serviced yesterday and asked the engineer about it, but he said it was probably the Heat Exchanger & it would be cheaper in long run to replace boiler.
ould it be the Boiler Thermostat. It acts same at any thermostat setting.
by the way, the pump runs OK when the boiler goes off & the pilot light goes out. (Hope this makes sense - I’m a bit thick when it comes to this sort of thing)
Would be most greatful for any comments.

13/12/08 @ 11:43
Comment from: Kevin

I just wanted to add my own thanks to the many others. A great piece of work. It’s been many years since I tinkered with a pcb so I needed to treat myself to a new soldering iron at Maplins. My repair costs were a massive £11.90.
Thank you.

18/12/08 @ 11:41
Comment from: stan

Hello all, Great blog. I have a simliar problem with my Potterton Prima F 50 and I want to know if its the same symptoms. The HW fires when I set the time on, but I get nothing from the CH system if its on and the themostat is set high. Could this be the PCB.

Thanks in advance

23/12/08 @ 13:47
Comment from: andy

hi, i have a potterton profile boiler 80el. I have the problem with the fan switching on and boiler tries to ignite but no fire then the fan goes off this is repeated over and over. I went to maplin and changed the caps. 1st just the fan came on and that’s it. then after checking the APS the normal fan on/off started to happen so i tapped the pcb black box and bingo there was light… but now i have to tap the box for the boiler to light….. do i need to change anything else on the pcb. can anyone help. btw i’m tapping the pcb with a plastic ruler :P think there a lose connection to something dont know what…?

02/01/09 @ 12:40
Comment from:

Sorry for lack of follow-up recently - I moved my blog to a new server in early December and it’s failed to forward me notifications of new comments since.

@Chris, sounds like a thermostat problem to me - either main stat or pump overrun according to the troubleshooting chart. I can’t see why the heat exchanger would cause that problem directly. I suppose that if it was working badly it could cause one of the thermostats to cut out before the whole circuit had reached temperature, but it sounds a long shot. It’s a fair question for him to question if it’s economical to repair - by the time you’ve got the CORGI man in and paid for a new stat, it’s probably at least a couple of hundred quid. Hard to judge if it’s worth it for an old boiler. Capacitors are one thing, but thermostats are well outside my comfort zone!

@Kevin, thanks!

@stan, since it’s specific to that one circuit, it sounds very unlikely to be PCB. Sounds more likely to be the actual room thermostat to me, but I’m not a heating engineer.

@andy, I guess you could see that with a dry joint pretty much anywhere on the PCB - the tap could be enough to remake a failing connection. If it were mine, I’d take out the PCB and re-melt every joint on the underside with a hot soldering iron to rule it out. Good luck!

04/01/09 @ 16:47
Comment from: Chris

Many thanks for your comments, I think we are going to let the Potterton run on (if it will) till it gets a little warmer and then go for a new boiler. It’s probably about time.
Thanks once again,

05/01/09 @ 13:57
Comment from: Andy

thanks nick but before i started to re-melt all the joint, i found a new PCB @work there were replacing there boiler which to my luck was same as mine profile 80el working perfectly. so took the whole thing for parts. Changed the PCB and it fired up perfect but few hours later same problem fan on and off but this time without any tap to the pcb it fired up by it self after a few clicks. I did notice a difference that the pilot light stays on all the time on my boiler and with the work boiler it was out. next door also has a potterton and there pilot is off too. do u think gas valve might be the problem? as have been told el means electric ignition and pilot should not remain let….? some help please

06/01/09 @ 14:20
Comment from:

@Chris, hope it lasts!

@Andy, I don’t have much useful to add I’m afraid - it sounds different from mine anyway. I’d work the troubleshooting chart (link 3/12 above) right from the start without any assumptions. I recall that I misdiagnosed mine because my pilot started alight. If you’ve swapped the PCB though it’s very unlikely to be that!

06/01/09 @ 16:17
Comment from: ian k Ferguson  
ian k Ferguson

HELP !! …fantastic helpful guidance, .. any chance there is a similar thread for my Vaillant ecoMAX pro 28E open vented condensing boiler : fan starts, sparker sparks, pilot/burner fires for about 2/3 seconds then goes out,.. repeats another twice, then shows IGNITION fault, .. or it just fires up fine and works for days , .. then falls over again??

08/01/09 @ 09:04
Comment from:

@ian, unlikely I fear; the accumulated wisdom here is rather specific! Other commenters have recommended, and I’ve found much useful guidance on the Usenet group uk.d-i-y in the past. Good luck!

09/01/09 @ 15:12
Comment from: Al Curnock  
Al Curnock

So glad I found this blog . Just saved me £120+.
My Profile 30e had been getting progressively worse and worse, taking upto 5 minutes of multiple attempts to fire up. This had previously happened about 3 years ago at which time I had a new control PCB fitted (cost around £120 if i remember). Swapping the 3 caps this time solved the problem instantly and only took me about 20 minutes all in.
One other useful point to add. the PCB has been thoughtfully designed such that C6 & C7 can be replaced with either a radial or an axial lead component - see the printed component outline on the PCB. Useful if you cannot get hold of the one as originally fitted. And i agree with fitting 105°C ones - the originals on mine were only 85°C rated.
Cheers !

10/01/09 @ 09:11
Comment from: Ken

Hello, I’m having trouble with my Profile 50e. The problem sounds similar. The fan starts but then continues to run, the igniter doesn’t start. Is this likely to be the Control Unit?

Thanks in advance.

10/01/09 @ 15:18
Comment from:

@Al, thanks!

@Ken, if the fan is running, not cycling, then it’s a different fault. The troubleshooting chart is linked several times on this page.

11/01/09 @ 01:54
Comment from: Andy

Guys if u remember i wrote a post regarding profile 80el. Changed the caps but nothing still the same problem. Well British gas corgi engineer came round and found the pilot was still on even when the boiler was switch off. He blew it out and bingo switch on 1st time then again it stayed on and the fan kept on switching on and off. Anyway after changing the gas valve everything was OK pilot switch off and only came on when boiler was switched on. SO CHECK YOUR PILOT if that stays on then problem is with the gas valves. Although the engineer did say most problems are with the PCB but check. TIP! what you can do is take out the homecare 100 and when the engineer comes to check and do his 1st visit they tell you whats wrong with the boiler if anything they normally don’t cover you if things need to be changed and cancel the policy meaning you can swap the faulty part yourself with free advise :) and if they say all is OK when you know its not working properly then u can call them out again after few days and they repair the part for free only £15 per month direct debit ;)

14/01/09 @ 14:25
Comment from:

@Andy, cracking tip. Thanks very much for that!

14/01/09 @ 14:47
Comment from: Dabs

last post 05/12/08 @00:52
An update for knowledge purposes.

Following on from the initial board change (which resolved the fan cycling problem), the second problem (ruuning for 1 min & cutting out) was finally found to be a faulty diverter valve on the hotwater side. Once changed everything was running fine………..or so it seemed until now.

Couple of days ago the boiler completely packed up. No response or heat or HW demand (completely dead -no fan etc). Followed the Potterton fault sheet and checked all the voltages specified and was lead to the air pressure switch (see potterton fault finding sheet, it either recommends fan change or air pressure switch change). Just before changing air pressure switch thought I would try the old faulty PCB (the one with the original fan cycle problem), guess waht it gave me a response and I got the cycle problem again - which I guess indicated at least the fan is ok even though I suppose air pressure switch could still be faulty. Anyway, to cut a long story short I went back to the heating shop and exchanged the conked out PCB (the one that lasted a month) and hey presto we are working again with a new PCB.

So for ref, a completely dead boiler could also be a faulty Main PCB, not just a fan cycling problem. Will keep an eye on the system now. In the mean time I hope this helps.

16/01/09 @ 07:36
Comment from:

@dabs, sounds like your Potterton has more than its share of troubles! Thanks for the extra feedback. It does make sense that if the PCB is completely caned then the boiler won’t work. I presume it’s rare though for it to die totally, since there’s not any particularly complex electronics there. You must just be lucky!

16/01/09 @ 15:53
Comment from: jon

Thank you and thank you to dabs the comment above mine. My profile 30e boiler just died completely, the symptoms were no fan, no ignition nothing. Having read your info and all the other comments i decided to have a go. 33 pence later i now have a fully functioning boiler and a happy family!

Not only have i saved on not having a new pcb but i have also saved on the weekend emergency call out charge!

17/01/09 @ 10:01
Comment from: Dave S  
Dave S

Having read all the info above, it all sounds very promising, so I will be visiting Maplin tomorrow to get the required components C4, C6, C7, R15 and Z3.

Just wondered. Do any of you guys that have done this exercise already, happen to have retained your bill for the purchase? If so, it would certainly be useful (to myself and other sufferers) if you could list the Maplin part numbers of the above components. Many thanks to dr-nick and all of you others!

04/02/09 @ 10:10
Comment from:

@Dave, fair point; I haven’t myself. One thing to bear in mind is that Maplin have quite a variety of parts which will do - typically at least 3-4 different components any of which will do the job perfectly well. Whilst it may not be a problem online, when I went to my local(ish) store, they only had limited items in stock, so I ended up with second or third choices. So, in store at least, you’re probably better to know the spec, and then see what’s behind the counter rather than be fixed on a particular part. Hope it works for you. Let me know (and by all means give part numbers!)

04/02/09 @ 15:03
Comment from: Dave S  
Dave S

Hi Nick, I did some further research last evening, and now have Maplin part numbers for all parts except Z3, the zener diode. So hope this helps others in need:

Description MAPLIN PCB Ref
22uF 63V axial capacitor AT04E
22uF 63V radial capacitor VH28F
4.7uF 63v radial capacitor VH19V
100k Resistor D100K R15

As far as the zener (Z3) is concerned, someone had read a number of W03C51. This appears to be a part of spec number BZW03C51 which seems to be a 51 volt zener diode. I couldn’t see anything on Maplin’s website that looked like a safe compatible part.

Rather than risk further problems I intend to go for the above components and refurbish and check the soldering of the board.

Meanwhile adjusting some of the controls (increasing pump speed, and reducing thermo setting from MAX (wife’s idea of how they work) to 4) seems to have given me a stay of execution as the button hasn’t popped out for 15 hours or so.

05/02/09 @ 07:00
Comment from:

@Dave, thanks for this. The Zener is relatively unlikely to fail as it’s much less sensitive to thermal environment. If there’s not evident scorching, I’d probably trust it to keep going. Good luck (especially if the weather with you is anything like here!)

05/02/09 @ 07:28
Comment from: Jon  

Dear Nick,

Just a quick note to say how glad I am to have found this site and to thank you and the rest of the budding heating engineers to have commented on your site.

I was in a desperate panic when my old boiler decided to fail on the 8th Feb 09. It is the same model as your’s and suffered from exactly the same symptoms i.e. failed to light, fan running etc etc.

Faced with the prospect of an expensive call out, I searched the net and there you were.

Without hesitation, I disassembled the cupboard to gain access to the boiler and began the strip down of the board. Your instructions were so informative even a novice could attempt the repairs let aloan an experienced aircraft engineer!

On the way to work, I broke the bank at Maplins and bought the capacitors and 100K resistor, all for 0.74p. I got the board under a magnifying glass and found the 100K resistor R15 looked to have suffered from a bit of overheating and loose in it’s mounting, although it’s resistance was still OK but I replaced it anyway. Also 1 of the 22uF capacitors was only 4uF so I replaced all 3.

Got the board home again (to a very cold house, 1 cold wife and 3 frozen kids) wondering if it would work. It took about 10 mins to re install, I kept my fingers crossed and…………………… God it fired up first time! Not only that, the rads are now scorching hot and I am turnig the boiler stat down. How can that be? Has the boiler had a problem for a long time?

I would just like to say a big thank you from my family and I for saving us a large amount of money which is required elsewhere. If you were local I would buy you a drink.
It’s great to know there are still people out there that want to help others without ripping them off!!

Thanks again.


09/02/09 @ 15:50
Comment from:

@Jon, thanks, I’m glad you’re all feeling warmer!

09/02/09 @ 16:34
Comment from:

I’ve just realised that this page has now been up for a year. In that time, it’s been viewed over 3,500 times, and helped many people, who have offered kind words, which has given me great pleasure.

On a night like tonight with inches of snow on the ground and temperatures below zero here in the Midlands, it seems that perhaps there’s an opportunity to make good in another way.

To that end, I’ve decided to add a ‘donate’ link. I hope this will help to cover my site hosting costs, and also contribute to National Energy Action, the UK charity which fights fuel poverty. So if you’ve saved yourself a hundred pounds or more by browsing here, please consider giving a fraction back. I’ll post back here as and when there’s a significant milestone to report.

09/02/09 @ 18:08
Comment from: Rich

My boiler has been cycling for about 12 months now but tonight it finally packed up. I’d bookmarked this site in anticipation of it eventually failing. Yet another boiler fixed. Great advice. dr-nick.

20/02/09 @ 21:16
Comment from: Gary

Had the same problem and although I have a maintenance contract with House (British Gas, not the TV show…) and they were coming out on Monday I am an electrician by trade and have done a lot of electronics so thought I would have a go…I was bored. Did it Friday night and it made no difference…no problem I thought…however Saturday morning the boiler fired up first time and has done so ever since. Canceled the call out on Monday. I can only think the boiler not being called upon all night on Friday must have had some sort of effect and then first thing in the morning was like some sort of “reset"…weird but its as solid as can be now…fires up instantly…go figure….

But thanks for the tips guys….

22/02/09 @ 14:34
Comment from: Gary

Just an update on Sunday night. Boiler still firing up every single time. So changing the capacitors has obviously worked…no idea why the 12 hour delay in it working though but I don’t mind.

22/02/09 @ 22:38
Comment from: Happy Chappie
Happy Chappie

Just experienced the same problem on my Profile 50e which began to play up over three days. The boiler firing up for short bursts or not at all and gradually getting worse until nothing.
A trip to Maplins for 3 capacitors, just over 50p, a bit of time spent taking the PCB card (all instructions above were great), I did resolder all the joints for good measure as comments of dry joints is also a known intermittent problem. Boiler working great. An excellent help page well done

25/02/09 @ 13:00
Comment from:

@Rich, @Gary, @Happy Chappie, glad it’s worked for you all.

Over 4,000 views for this page now. Gosh!

26/02/09 @ 10:54
Comment from: dabs

last posts 05/1208@00:52 &16/01/09@07:36

Looks like my mate the 80e is up to its old tricks again. The ‘2nd new’ pcb control board has been working ok, until now. What happens now is, system (both CH & DHW) runs ok (after firing up 1st time) for over an hour and then biler just stops and refused to come back on again. Wait for a while and retry several times and it may fire up again or not…depending on its mood.

I tried changing the pcb again for a reconditioned one I borrowed and, hey presto, thought that did the trick. But this time got the fan cycling problem about 3-5 times before boiler kicked in and it worked for a while again and then got the same cut out problem. So, I put all the kitchen knives away……, and then put the orginal pcb back in. Outcome…exactly same as above…ie reinstalling the 1st pcb gave me slightly different results!!! Got the whiskey out and carried on..

Went through all the fault finding stuff and decided to change the Air Pressure Switch (APS). Now I have a boiler that waits upto 30-40 secs to do anything (ie no response) when an inital heat demand is made, and then after several fans cycles it fires up & runs for around 15 minutes. It then starts to switch on and off at very short intervals say off for 3 or 4 minutes, fan cycle 4-5 times then a 1 to 1.5 minute burn. The rads and water do get hot but clearly it’s not working ok and probaly costing a lot more to run.

Has anybody got any ideas, I don’t think its the PCb’s, or APS related having changed these. (I have noticed the rads are not getting hot at the bottom so I think I got sludge problem that needs sorting), but shouldn’t cause this should it.

Anyway any input, even ‘change the boiler would be appreciated. I don’t particulary want to change the boiler as the las one on the local Heating guys said it was a pretty relaibe model overall + boiler and power flush will set me back £2000. Alos, do you think I can powerflush myself, or does this require CORGI.

06/03/09 @ 12:44

Hi Dr-Nick, Many thanks for this step by step guide, it’s been very very helpful.

I was hoping somebody may be able to help me. Before I took out my PCB to repair, I noticed that there was a yellow wire which was connected to the back of the thermostat control knob on the boiler…now the other side of this wire was not connected to anything, it looked like it had been cut off from somewhere. Here is a photo I took -

Ignore my finger, I have added red arrows next to the wire im talking about. Im just trying to find out where this wire connects to. It does look like its some sort of earth connection? But the wire is not yellow and green (just yellow). I think I can just about see it in one of Dr-Nick’s photos, but its not clear where it is going. Do you have any ideas? Or even a photo so I can see where to connect it to?

Many thanks

08/04/09 @ 09:42
Comment from:

@ChrisL, I can try to remember to have a look when I get home again, but it’d be useful to know what it’s attached to at the end behind the knob. If it’s just screwed to the metal supporting plate then for sure it’d be an earth connection.

08/04/09 @ 11:04
Comment from: Chris  

Thanks for the reply Nick. Yes, it looked like it was attached to a small plate…so looked like an earth connection. I just dont know where it connects to as the other end of the wire did not have a connector or any exposed wire…like it had been pulled from somewhere. I will have another look at it when I get home. Many thanks

08/04/09 @ 11:13
Comment from:

@ChrisL, looks very much like an earth to me. Here’s a photo of the PCB swung down; you can see the yellow wire connecting to what looks like a rivet point on the backplate adjacent to the connector block. I’d guess you’d be fine to connect it to the earth point behind that block instead. Usual disclaimer applies!

Potterton wiring

08/04/09 @ 22:06
Comment from: Paul H
Paul H

Superb write up of the repair of the frequent attempts to light problems of the Prima F. We had a similar problem in 2005 and Potterton took some weeks of visits - about 8 as I recall to repair. This time it took me just 90 minutes. In my case C7 simply had a poor solder connection.
There is a detailed circuit diagram in the grey plastic box which is pulled out after undoing the retaining screw at the bottom.
In answer to the question regarding the yellow wire, it does attach beside the 6 way strip connector. The black plastic rivet holding the wire has a central rod which can be pulled out and then you can push the rivet into position.Reinserting the tiny black rod open the wings of the rivet holding it in place.
Many thanks for the magnificent write up Dr-Nick, and Happy Easter.

12/04/09 @ 11:52
Comment from: James

I am so happy I found your site. Went to Maplin, got the 3 bits and paid just 65p!! Got home last night, got out the trusty gas solder iron and away I went. After soldering the 3 parts in I re-soldered about 6 dry joints and re-assembled the lot. Power on and Whoosh, on came the flame and heating was restored. Took me no more than 45 minutes (boiler was in really awkward place so getting PCB out was fun!).
Thank you so much for your write up on this, you are a STAR!!!

28/04/09 @ 10:37
Comment from: Nick

Thanks to all the contributors to this site, I had a similar problem on a PrimaF (50KBTU).Everything appeared to work OK ie fan, call for heat, pump running but no boiler ignition. went through ssequence whilst looking at control PCB and saw mulpiple sparks. The quality of soldering on the PCB is really poor, remade a few joints and the bolier resumed to service.

I must stress this was not complicated, but I am an electrical engineer so please dont attempt work unless you are competent and always make sure you isolate energy supplies before undertaking any work.

Thanks Again - top website!

14/05/09 @ 18:14
Comment from: Chris

Have you told the people on this site that by opening their own boilers they are breaching gas regulations? Probably more of interest, if they cause a boiler fire through this type of illegal work, they will invalidate their house and contents insurance. What will you suggest next?

22/05/09 @ 01:09
Comment from:


Thanks for your comment. As someone who considers risk carefully, I’ve read the gas regulations. I do not believe that the work I conducted breaches them. If you read the post you’ll see that I’m quite clear about obligations for landlords and employers. I do not advise opening or touching gas fittings. If you can reference where in the gas regs it states that it’s illegal for electrically competent domestic users to repair the control boards of their own gas water heaters, I’ll gladly review the post.

The insurance point is well made. I will amend the post to be clear about this risk.

22/05/09 @ 10:09
Comment from: ChrisA

Many thanks Dr Nick. My Prima 40F is now up and running after a couple of days thanks to your info. R15 looked a little scorched, and there was a completely dry (no solder) joint on one of the larger multi connector pins. I also replaced C4, C6 & C7 as recommended - the radial 22uF was down to 4uF. The Maplin spec’d caps are good up to 850degC according to their spec sheet.

Even with buying a new iron & desolder pump this came to a grand total of just under £30.

Thanks again!

31/10/09 @ 21:25
Comment from: Paul H
Paul H

Dr. Nick"s comments about safety are entirely correct. The Prima’s electronics is separate to do the gas supply, and removing the PCB from a boiler as described above is in no way any more dangerous than repairing a PCB in any other electrical device. The important requirement from the point of view of the gas regulations is not to alter the gas system, and there is no such suggestion above.
This blog is probably one of the best on the internet, as it has helped countless people repair their boilers as the comments indicate.

12/11/09 @ 21:51
Comment from: Tony

Hi Dr Nick, I’m VERY impressed with your blog and results your readers have obtained.
I have a Prima F 100 that has run fautlessly for 13 years until recently the overheat sensor started popping out. Then I noticed when starting from cold, the boiler was going through multiple 10 second start up cycles before finally completing the fire up sequence. Once hot it seems to start up first time.
When it’s going through multiple cycles the fan starts up but the sequence does complete to light the pilot, it cycles down before getting to this point. Once it gets to the point that sparks and lights the pilot the burner fires up very soon after and all is well.
I have been advised if the cycle time is 2 - 3 seconds it’s the PCB, if it’s a 10 second cycle its the AP sensor or associated piping - or a blocked airflow restrictor (fitted to clear pipe close to AP sensor) . Checked all of these and still the same problem.

Can you advise if your experience with the faulty PCBs showed cycling times of 2-3 seconds or about 10 seconds?

Once I have resolved the cycling problem I’ll have to work out whey the overheat trip sometimes pops out.



03/12/09 @ 21:24
Comment from:

@Tony, for me it was about 3 seconds cycle time. Good luck!

03/12/09 @ 22:03
Comment from: Tony  

Nick, thanks for your prompt reply. Looks like I may heve to check the AP switch to see if it’s diapragm is leaking.
Will still chack those capacitors on the PCB anway, local maplin is only 3 mins away. :-)

03/12/09 @ 22:49
Comment from: Tony  

Hi Dr Nick,
More on my dodgy Prima F 100: I re-read your introduction and noticed your had advised the fan ran for about 3 seconds before cutting out.

[I had been advised from elsewhere that a 3 second cycle time indicated a PCB fault but a 10 second fault indicated an APS fault.]. The boiler made multiple attempts to fire up from cold and usually it eventually fired up after 10 to 20 cycles. Once hot it worked fine normally firing up first cycle.

Nothing was wrong with the APS or pipes, air restrictor etc. So I re-thought what might be wrong.

I had mentioned a 10 second cycle time (in which the fan ran, stopped and then re-started). The fan run time was about 3 seconds so I decided to remove the PCB and replace the capacitors and R15 anyway, at least that would eliminate the PCB from the fault list if the problem persisted.
There were several dry joints too so I re-soldered most of the joints.

… Put it all back together and hey-presto, it now fires up first time from cold.

Your blog has saved me a lot of time and money - cost of capacitors and a resistor from maplin was about 70p.

Very many thanks. I have donated a fiver to your blog to show my appreciation.

Thanks agin, Tony.

05/12/09 @ 16:16
Comment from:

@Tony, thanks for that. Good to get the feedback, and the donation is welcome too!

05/12/09 @ 22:53
Comment from: haso

I have a profile 50e.PCB 407677 in front of me , with what looks like a burnt R15 which sits next to relay RL2.replace the 3 capacitors and R15. Put the board back in, and fired up. Many thanks to dr-nick and to dave s for Description and all of you others!

15/12/09 @ 00:31
Comment from: Les  

First I must say what an informative site! I have a 50e that has given me various bits of grief over the years, it is fitted in my garage (where we lived while doing my barn conversion). when i bought it s/h it wouldent work and Yes I had to change the board (around £120 at the time!) last year it failed to work and i simply put off doing anything about it. This spell of cold has prompted me into action! the problem this time is, turn on, fan comes on and after a short time pilot light ignites and stay on but main burner does not ignite, i must say i suspect the gas valve but would appriciate the experience and the knowledge I have seen on the site. many thanks.

21/12/09 @ 22:54
Comment from:

@Les, if you look at the troubleshooting chart in the installation guide (linked near the top), it suggests that if the pilot stays lit and the sparking stops, then the first thing to check is solenoid GV2. I’d check the chart for yourself, but that sounds a likely culprit. If so, it may be sensible to get a call-out, as I suspect you can’t replace the solenoid with out interfering with the gas line. Best of luck, Nick

22/12/09 @ 10:00
Comment from: Moose

OMG, what a major help this site has been. I am very grateful for the step by step instructions and pictures on how to remove and replace the PCB. I don’t have the nous for the circuitry soldering so I just bought a reconditioned PCB for £30. In 5 minutes the new one was in and the boiler fired right up. Many thanks from a happy and warm place.

23/12/09 @ 19:03
Comment from: Nigel Dawson  
Nigel Dawson


I have a Potterton Prima F boiler which had the PCB replaced 15 months ago. Recently the heating and hot water has started going off despite the timer being on. Sometimes by turning the temp control on the front it would re fire but recently this is not the case. it now has a mind of its own, if left it will start up randomly and run for a number of hours without a problem (assuming the timer is on) and then shut down at anytime.

After the boiler has shut down the fan still runs but there is no spark to the pilot. By adjusting the thermostat control the fan will stop and re start as if the boiler is going to fire but no spark. Walk away and a few hours later the heating is back on!

I have checked the PCB and all soldier joints look new as I would expect from such a new PCB. Is it possible that a 15 month old board could already be suffering from the capacitor problem?

Any help would be much appreciated.

27/12/09 @ 02:28
Comment from:

@Nigel, you don’t say whether your fan is cycling. That could point to something else. Check the chart to be sure (page 32 of installation guide, link in article). However, intermittent/random lack of firing can precede a complete failure as the capacitors degrade.

As to the age, bear in mind that the PCB could have been sitting in a bag on a shelf for 15 years before getting fitted to your boiler - there’s no guarantee that it was new when fitted to yours.

Best, Nick

28/12/09 @ 09:26
David McLeay

this seems like an excellent post which I have discovered just after solving a similar problem.

I have a Prima 50F boiler - it wasn’t lighting at all.

I turned the thermostat dial on the boiler down to zero, turned the control unit to off then turned off the electric supply to the control unit. I then resumed electric supply, turned unit central heating to on then turned up the boiler thermostat to max. You could see the pilot sparking through the glass window on the boiler and it kicked in.

My problems started a day after various power cuts - no idea if connected.

Good luck all.


01/01/10 @ 12:09
Comment from: Zeb

Lots of really good advice on this thread. Actually, this is the most informative thread on the interwebs regarding dodgy Potterton boilers! ;-)

I would also add that the transistors driving the gas valve relays can fail (been there, done that), and that the other one also causes igniter problems.

There are 3 BC307B transistors, any of which can, and do, fail. Any general purpose PNP will do the job. Replace all three transistors while you’ve got the soldering iron out. 3 quid, sorted.

Funnily enough, my own boiler is doing the 3 minutes on then 5 second reignite game. Even funnier is that my ‘new’ replacement board is useless. I could send it back, but of few minutes and a few quid of components …


04/01/10 @ 20:41
Comment from:

@Zeb, thanks!

Good tip on the transistors. I’d guess they’re less likely to fail than the electrolytics, being solid-state, but certainly worth considering. If you, dear reader, do replace them, remember to note the orientation of the original before you take it out - there’s usually a little metal tab which sticks out near to one of the three pins - make sure the replacements go the same way round.

As a side note, this page has had over 10,000 visits as of today. Glad it’s been of help.

04/01/10 @ 22:15
Comment from: Ben H
Ben H

With all the freezing cold weather and talk of boilers recently, I decided to scout around Google for info on my boiler - just to see if it was a good/bad/popular/temperamental model.

Stumbled upon this article. Very useful indeed - had no problems with my boiler yet but this is good information to have at hand - just in case!

I have probably jinxed it now, however : )

05/01/10 @ 13:17
Comment from: Zeb

Re: Transistors: The ones that I’ve seen on the control board are the in TO-92 plastic package, so you need to note the ‘flat’ side. I wonder if the reason for failure is that the back-EMF killer diode on the relay coil has gone open circuit. Can’t remember if the flybacks are seperate or internal to the relays (I hope the former case!). I didn’t use BC307Bs, but ones with the same hFE but with a higher Ic and Vceo and the hope that they might be more robust.

Oh, 10k visits today? There must be a lot of dodgy Pottertons out there!

05/01/10 @ 20:15
Comment from: imo

Dr-nick i replace my PCB with sec-hand PCB about 2 weeks ago
overheat sensor switch popping out.but boiler is working better than before. would you please tell me if is safe or not safe working the boiler without overheat sensor.

11/01/10 @ 00:38
Comment from:

@imo, you’re joking, right?

Given that the basis of this post is that overheating components are a Bad Thing, you won’t be surprised if I think an overheat sensor is essential. If the sensor is faulty, get it fixed. If it’s the boiler overheating, be glad that the PCB gave you warning.

11/01/10 @ 17:23
Comment from: james

Note of thanks to dr-Nick. -5 outside, boiler finally decides to not start - quick search on web for some kind of manual start to our potterton profile, and I found this great site

New capacitors fitted (cleaned up some other dodgy looking joints), unbelievably I did not made a mess of it and it started first time! overwhelmingly happy to not have flushed few hundred quid down the pan with engineer call out charges etc.

Still can’t believe how widespread the problem is, even a guy at work had same problem after i mentioned it to him .. ..

11/01/10 @ 23:39
Comment from: imo

hi Dr-nick
sorry problem is not overheating mistake.the problem is overheat stat .Red switch popping out. would you please tell me if is safe or not safe working the boiler without overheat stat.

11/01/10 @ 23:48
Comment from:

@james, thanks!

@imo, I’m not a heating engineer, so please don’t ask me for legally definitive advice on safety. However, common sense says to me that removing the overheat stat would be recklessly stupid.

Without the stat, your boiler won’t know if the water is getting too hot. As water gets hot, it expands. If it heats towards boiling inside a pressurised system, the system risks failure or explosion. Call a Gas Safe engineer and point them towards that stat. It will be more expensive to replace than a couple of capacitors, but far cheaper than repairing your house and the legal bills from your neighbours.

12/01/10 @ 07:38
Comment from: Zeb

Regarding the BZW03C51 zener (Z3), I’ve seen the 1N5369B used on this control board. Not available from Maplin, but generally available (try ebay).


14/01/10 @ 12:18
Comment from: SKUNKYDOG  

First things first .FANTASTIC SITE ,GREAT JOB
Two questions I would like to ask
1) I have tried to get the three capacitors from Maplins and havein place of beeen told there is difficulty in supply (must be a lot of Potterton boilers getting fixed).Can someone advise if I can use 22 uf 100v in place of the recommended 22 uf 63 v ( Maplins ref VH29F instead of VHF28F. Not being an electronics expert I would appreciate some advice.
2) The component SP-1 (next to the relay) seems to arc when I finally get the boiler to spark and ignite….Is this supposd to happen or should I replace this part when I have the PCB out.If I do need to replace it can someone please advise a part number /identification

14/01/10 @ 20:48
Comment from:

@skunkydog, if 63V works, then 100V will be fine - it means that it’ll tolerate a higher voltage on the board.

As to SP1, no idea what that is, I’m afraid! I assume it’s part of the spark generation circuit - from the photo looks like a coiled component, so perhaps an inductor? If no-one passing through adds a comment, I’d suggest perhaps it’s worth taking the board itself into Maplin and seeing if the folks there can identify it. Please post back if you find out more. Good luck!

14/01/10 @ 23:06
Comment from: Zeb


I’d recommend 100v caps - The circuit runs at 51Vdc and generally I’d recommend caps at twice the nominal supply voltage. Yes, 100V is better. I’d also try and find 105C rather than 85C caps - Must get hot under that burner chamber! Lot’s of other components ‘on the edge’ in this design. I’m working on an upgrade kit to be sold via ebay or something.

SP1 - If it seems to arc continuously, you still have a board fault. It should stop once the main burner is lit. Also check if the spark gap in the burner chamber is continuously, erm, sparking. If so, you’ve still got a board fault.

Got another board in to try today - Will see how it goes and how well my upgrades go on an old board.


15/01/10 @ 21:03
Comment from:

@Zeb, nice one, thanks! What do you think SP1 actually is, btw? I’m reluctant to open up my currently working boiler to take a closer look :)

15/01/10 @ 22:07
Comment from: Steve

Hi Dr Nick,

Just wanted to pass on my gratitude for your excellent work. My Prima F40 had been playing up for a couple of years and with the recent cold weather was reluctant to start at all (1 hr + of cycling before it would fire, if at all). Having resigned myself to an expensive engineer visit I was researching my options on the interweb when I came across your page. Like others have said, 74p at Maplins and an hour of my time and hey-presto instant heat! Hardest part was removing the PCB from the boiler which took most of the time.
Anyway, brilliant work and thanks for sharing.

16/01/10 @ 13:28
Comment from: Lindy

Hi Dr Nick

I have a Potterton Neataheat Profile 30e. The ignition sparks and the fan is working but the boiler does not fire up. I had a new PCB fitted in April last year. Do you have any idea what the fault can be, your assistance would be gratefly appreciated.

26/01/10 @ 22:07
Comment from:

@Lindy, you don’t say whether the fan is cycling on and off, or running continuously. Take a look at my earlier response to Nigel.

26/01/10 @ 22:32
Comment from: Geoff  

Hi - adding my experience - I have a potterton netaheat 60e.
It started tripping out (overheat sensor) - requiring the button to be pushed up (from underneath) to reset it.
It previously only very occassionly tripped out and then generally when I had the boiler thermostat up (to 6 or Max). Over the last couple of days it was tripping out all the time - every hour or 2 I would check it to find it had tripped again.
I took the circuit board out as described above and ran a soldering iron over every joint on the underside of the board - its very possible that there were a couple of dry joints as I had a couple of joints that didn’t re-solder that well at 1st.
I also noticed another potential problem. There is a presssure switch (also visible when you have removed the bottom cover) - is a white disc shape about 1-2 cm thick with 2 plastic tubes connected to it (one red) - one of these tubes was routed such that it had ‘kink’ in it which would be obstructing the flow in it and could presumably affect the operation of the pressure switch. (Apparently this switch is a safety feature which determines what the pressure is on the flu to prevent any exhaust gasses coming into the house.) I don’t know whether this would lead to the trip outs but I routed the tube so that it wasn’t kinked.
A day later and my boiler hasn’t tripped out!

27/01/10 @ 18:31
Comment from: Lindy

Hi Dr Nick

The fan runs continuously and the pilot sparks but does not light up. I have read Nigel’s comments and I didn’t have any problems with the boiler starting up and going off on its own. It worked perfectly well until yesterday morning when it just would not ignite. I have tried turning off at the main switch and turning off and on on the programmer but with no joy - can you help? Thanks

27/01/10 @ 20:14
Comment from:

@Geoff, interesting to hear about the pressure switch tubes. I don’t recall it being the same in my Profile, but if it helps someone, all to the good.

@Lindy, if the fan is continuous, it’s not the capacitor failure I had. I’m not a heating engineer, so all I can do is refer you to the troubleshooting chart in the manual (as I pointed you towards before).

If the pilot doesn’t light, it could still be another fault on the circuit board, but it’s more likely to be the solenoid that releases gas to the main burner which has failed. If you’re electrically competent, or know someone who is, then they could check the mains voltage on the appropriate terminals according to the chart, to rule out an electrical fault. I expect though, that you’ll need to get a professional repair. I’d recommend you print out the manual and give it to a CH engineer, opened to that troubleshooting page! Good luck!

27/01/10 @ 20:42
Comment from: Tony  

Amazing info on this page and a BIG thankyou to all that have posted usefull info here.

I had the fan spin up and then endless sparking going on but no pilot lighting up symptoms. Boiler is the Prima F 80 so wasn’t sure if it had the same board. Luckily its the same 407677 so before I rushed out to buy the parts, thought I would strip it first then see what was needed.

Resistor R15 had shed its outer clothes but was still 100k ohms. Lots of cracked solder on the main connector block pins so soldered them up again and refitted without changing any parts. This time pilot only took 15 seconds to light instead of the normal 15 minutes. I will be buying the 3 capacitors, resister and the zener diode z3 as it doesn’t look too good and see other folks are not in good shape either.

Problem is this doesnt seem to be a normal zener diode. No is BZW03c51 and looking at spec sheets on the net it says its a “Silicon Z–Diodes and Transient Voltage Suppressors“. Its is supposed to withstand certain high spikes probably from the sparking circuit. Will a normal zener not break down here?

Has anyone found an alternative and will the maplin one N92CA and if you scroll down particulary the 1.5KE39A 39V 29A 53.9V do?

03/02/10 @ 12:37
Comment from:

@Tony, I don’t feel confident to pass judgment on specific Zener diodes. However, all Zeners operate as transient suppressors when connected in their ‘reverse bias’ direction. Breakdown shouldn’t be a problem, as there should be a suitable resistor to ensure the current is kept low enough by design (see wikipedia for a simplified diagram if you’re interested). Zeners won’t suppress spikes in their ‘forward’ direction, but presumably that’s either not a problem or there’s another Zener in opposition on the board (can’t recall without looking).

As long as an alternative Zener meets or exceeds the breakdown voltage and power dissipation of the original, I’d expect it to be fine. Other commenters have mentioned 51V and 1.5W as relevant figures; your mileage may vary. Good luck, and let me know how it goes. Obviously if any other passing readers have definitive comment, it’d be welcome.

04/02/10 @ 07:50
Comment from: coyote_rich

This has been possibly the most useful page I’ve ever found on the internet. I have had exactly the same fan cycling problem on and off for maybe a year or so but it always lit eventually, until last night. After a bit of searching and looking around the Potterton website (which has some useful documentation) I came across your post. I got the capacitors this evening (costing about 75p) and by 9pm it was back up and running again. Thanks for posting it Dr Nick and Tony. Saved me a lot of cash. Lots of people must owe you lots of pints by now.

10/02/10 @ 00:09
Comment from:

@coyote_rich, thanks!

10/02/10 @ 07:14
Comment from: Dave M  
Dave M

Hi guys, urgent help needed please.. freezing household!

I have a potterton 50e.. and as of yesterday, it fires up.. then goes out after about 2 minutes. Then I have to wait ages untill I can re-start it.

it then does the same thing, shuts down!

is it overheating? or bad circulation?

One of our radiator pipes upstairs burst a few days ago and I repaired it.. but i think a lot of air remained in the rad (havent bled it yet)

would this be a contributing factor?

its an LPG boiler and we use gas bottles, but there is a full load of gas.

can anyone advise please



14/02/10 @ 09:22
Comment from:

@Dave M, the delay makes it sound like the thermal trip. If there’s consistently a couple of minutes of running, then it sounds likely that it’s genuine overheating (rather than faulty overheat stat). When it starts, see if hot water is reaching the other side of the pump in the first 30-50 seconds. If not, see if you can feel if the pump is trying to run. I wouldn’t be surprised if you need to flush the system and/or call out a Gas Safe engineer.

One thought - can you turn the boiler stat to minimum so that it doesn’t actually fire and still power the pump? If so, you can try to bleed that rad with the boiler not firing. That’d perhaps tell you if the pump and pipes are running as they should…

Good luck, Nick

14/02/10 @ 22:25
Comment from: Lindy

Hi Nick, my boiler has been repaired at along last. The engineer fitted another new pcb, a new pressure value and as a last resort (because it was still not working) a new solenoid - and yes that IT WORKED. Just as you thought it was, it was the solenoid. Thank you for your assistance I just wish my engineer had as much knowledge as you.
Thanks again

17/02/10 @ 10:42
Comment from: Ali  

Hi, Please help, I have a Worcester 14/19 gasfired boiler, it will not fire up in the mornings and takes about 20 minutes to fire in the afternoon. The fan runs, it clicks and the pilot light flares up and it then instantly cuts out, this continues to cycle until eventually it kicks in. The boiler is only 5 years old and has been serviced.

18/02/10 @ 09:16
Comment from:

@Lindy, thanks! Glad you’re warm again!

@Ali, if you read the post, you’ll see I have a Potterton boiler, not a Worcester. I’m afraid you’ll have to look elsewhere. Maybe a heating engineer?

18/02/10 @ 18:02
Comment from: clare

Hi, I have a potterton profile boiler which is causing big problems. Firstly it wouldnt ignite. Plumber said we need a new fan which he fitted. Now it ignites but the radiators are almost cold and the hot water is lukewarm at best. Do I need a new boiler or has anyone any suggestions. I cant afford £2,000+ at the moment.


20/02/10 @ 17:36
Comment from:

@clare, sanity check first: is the main thermostat at the front turned up? When lit, does it stay lit but just not warm up much? Between minimum and maximum settings, the hot water should be between around 55-80C. If it was a pumping problem, then I’d expect it to overheat and cut out, so the only other thing I can think of is burner pressure. Mind you, I am a complete amateur…

20/02/10 @ 19:13
Comment from: Tony Martin
Tony Martin

I had a problem om my Profile with the pilot not lighting reliably - sometimes taking a long time, sometimes not lighting at all. Previously I had fixed it by re-soldering some cracked joints on the board, but over time the same problem had recurred.
I found that Relay RL2 was not switching as it should, whereas tapping the board caused it to switch and the pilot to ignite.
The voltage across the coil of RL2 was only about 20V (Relay coil is rated at 48V).
The cause turned out to be capacitor C7 (the bottom one in the pictures posted earlier) and, having replaced it, the voltage at RL2 coil now measures about 35V and the relay switches when it should.

21/02/10 @ 12:48
Comment from: Blitz

Just replaced the 3 capacitors on my Profile 60E control board (407677) after boiler failing to ignite and the fan cycling problem. Now works perfectly. Maplin part numbers are AT04, VH19 and VH29, total less than £1. Many thanks dr-nick for your detailed instuctions and continued improvments (donation left) and to everyone else for their contributions to this site.

22/02/10 @ 13:26
Comment from:

@Blitz, thanks!

22/02/10 @ 17:24
Comment from: coyote_rich

Does anyone know what the start up cycle is for the Profile 30? I recently fixed a fan cycling problem with the replacement capacitors trick but it has now started to rattle at the very end of the light up process. What would normally be a loud tick of some component turning on or off is sometimes a rapid rattle as it opens/shuts/turns on/turns off. If I can figure out what the last operation is in the start up sequence it should point to the part that’s doing it. Anyone have any ideas?

25/02/10 @ 19:00
Comment from:

@coyote_rich, wild guesses only from me, but there’s not much mechanical apart from the two solenoids in the gas valve assembly. Perhaps the latter of them is on its last legs? One for a Gas Safe engineer, methinks.

25/02/10 @ 21:56
Comment from: Tony

The start up sequence for my profile 50 is (I think) as follows:
The Fan comes on and the pressure switch activates after a short while. RL1 on the control board switches and locks mains supply on. RL2 switches over to charge the spark circuit and the pilot light solenoid is powered by connecting one end to neutral. Once the pilot is lit RL2 drops back to it’s non-activated state stopping the spark and powering the main gas solenoid.
Thes are the only electro-mechanical components and the relays are obviously quiet compared to the solenoids.

01/03/10 @ 16:45
Comment from: Mary

We have a Potterton Netaheat Electronic 10/16 which we`d like to move, but the place we`d like to put it means it would need a flue extension as it wouldn`t be on an exterior wall any more. Of course production has ceased, so the flue extension is `unavailable`. Does anyone have any ideas?
I love this problem-solving site! Thank you so much.

03/03/10 @ 15:26
Comment from: NSingh  

Finally found your site which contained sufficent detail in order to carry out the repair on my Prima F. My boiler had the same problem described where the fan ran on continuously but the boiler did not fire up. The only way I could get the boiler to fire up was to open the white casing, wait for the fan to start and kink the RED flexi pipe which stopped the airflow. This would mean the fan stayed on and then I’d wait to hear the click from one of the relays on the PCB, then I’d remove the kink and put the casing down and the boiler would fire…no fun at 6am on a cold bitter morning :0(

Having found your site, I took your advise and spend 74p on the three caps but on the first attempt the repair failed. The boiler fan was staying on longer but no spark so I read your article further and noted that you had pointed out that the caps had to be fitted correctly taking note of which side was positve (+). I checked the caps and saw the + sign on C6 which I had fixed incorrectly. I changed that around and WHOOSH the boiler fired up.
Thanks for the EXCELLENT advise and many thanks taking the time to do the write up - You the Man!!!

04/03/10 @ 18:09
Comment from:

@Mary, first option would be to get in touch with Potterton. They’re still in business in Warwick and may be able to suggest an alternative. If not, I imagine they should still have the technical drawings. You may be able to commission an aluminium fabricator out of the yellow pages to make one to spec. What I would say is that you shouldn’t hack something together. You don’t want carbon monoxide and unburnt gas leaking from a badly put-together flue! Good luck, and post back if you come to a successful conclusion.

@NSingh, thanks! Don’t like the sound of the pipe kinking though - not something I’d condone…

04/03/10 @ 19:00
Comment from: Ped

A Profile 50e was displaying ignition problems, taking up to 30 attempts to light the flame bed. If it failed to ignite, the pilot would continue to feed its small supply of gas, which was expelled through the flue by the fan. This process would continue until the ignition process was restarted, by turning the circulating temperature thermostat off and then back on.

The three electrolytic capacitors on the PCB were replaced with high temperature components rated at 105 oC and 100V. The soldered connections for Capacitor C6 are very close together and great care is needed to avoid unsoldering adjacent components. All the replacement Capacitor bodies bore markings showing the negative (-) terminal, but the PCB concerned only indicated a plus sign (+) for Capacitor C4 to show which way the terminals had to be connected. For Capacitors C6 and C7, however, the positive (+) terminal location on the board was indicated by a black rectangle.

The problem was solved with the boiler igniting first time every time.

My Thanks and congratulations to Nick and all contributors

08/03/10 @ 19:18
Comment from: Tony

I thought it worth mentioning something I noticed when repairing my Profile 50eL (with the help of this thread).It might save others from becoming as confused as me.

As can be seen from pictures posted earlier there are 4 wires connecting to the gas valve (white, black, blue and Green/yellow). they go through a connector on the fold down control tray and then to the control board. So far so good, except that on my boiler (which has a SIT gas valve) the black and white wires are transposed at the connector.

The only reason for this seems to be to correct an error in the circuit diagram in the installation instructions which shows the white wire connected to gas valve EV1 (pilot) and the black to EV2 (main burner). This would be wrong and does not agree with the diagrams for boilers with other valve types.

Note that the fault finding chart in the instructions also has errors.

Can anybody confirm my observation and reasoning ?

29/03/10 @ 20:27
Comment from:

@Tony, I wonder if they changed the gas valve to be fitted as standard at some point during production, and so needed to change the wiring, but never updated the manual? Your reasoning seems fair, although as it’s not directly related to my problem/solution, I can’t corroborate.

31/03/10 @ 22:02
Comment from: Ian

I have read all the comments and suggestions but may have missed the one that has the same problem as me.

Heat demand
Fan runs continuous
Pressure switch activates
But no spark

I have checked the trouble shooting diagram and it asks if there is 240v across T2 and T4 - if there is changed the electronic controller.
I do have 240v across T2 and T4.

Is the solution different to changing the 3 caps. - all components look good on the board and I have re flowed any joints that look suspect.

31/03/10 @ 23:40
Comment from: Tony


There WAS definitely a change of gas valve at some point as the valve is apparently made by SIT whereas most of the stuff I found (including your jpegs) showed either a Honeywell or White Rogers valve, which look very different.
The installation & service instructions (publication no. 5107228), which the installer was good enough to leave me, shows this valve. Having downloaded the equivalent instructions for boilers with the other valve types, I found that the circuit diagrams in the new manual showed the connections to the 2 valves swapped over.
My first thought, as yours, was that the functions of the valves themselves had been swapped in some way but a little bit of investigation showed that valve no.1 was still the pilot & valve 2 the main burner. (note also that the valves are called EV1 & EV2 rather than GV1 & GV2)
Hence my conclusion that the swapping of wires was to correct the error in the manual.
Incidentally, there is no way that the thing would work if the wires were swapped back and I think it would be rather a dangerous thing to do.
Bottom line is that all the comments posted in this thread are still applicable and the actual connections to the gas valve the same, the changes only become apparent if you dig deeper into the wiring.

01/04/10 @ 09:28
Comment from:

@Ian, do components “look” good or test good? One commenter mentioned transistor failure before - that would be T2, T4 which might be why they’re referenced in the troubleshooting guide. I don’t know for sure though.

@Tony, thanks for the detail.

05/04/10 @ 09:06
Comment from: Tony Martin
Tony Martin


I think dr-nick has taken your reference to T2 and T4 to be to transistors whereas you actually meant the connector terminals on the board. What you are measuring is the voltage on the coil of the pilot gas valve. In any case if you do not see a spark you have already proved that the fault is in the electronics since the spark is also supplied from the voltage on T4.

Check out my post on 21/02/10 it might be the same thing ie Relay 2 not switching.

Measure the voltage across T1 & T2 - if it is zero then the relay has not switched over and the spark generator is not charging. If the voltage is 240V or thereabouts then the relay has switched and you should be getting a spark, so the cause must be elsewhere.

If the relay does appear to be not switching give it a tap - in my case that was enough to make it switch and give a spark.


05/04/10 @ 14:56
Comment from:

@Tony, Aha! Good tip.

05/04/10 @ 15:13
Comment from: Ian

Dr nick and Tony
Thank you for the advice.
I measured across T1 and T2 and got 240V, so the relay is OK.
So I think I’ll have to send it off to be refurbed by somebody - I just hope it is the board.

Thanks again

07/04/10 @ 20:42
Comment from: Tony Martin
Tony Martin


You have pretty much confirmed that the fault is on the control board.
From your earlier post it seems you have been following the fault finding chart so, assuming you have eliminated the electrode and it’s wire and cannot see sparks where they shouldn’t be, you have pinned the fault to the control board.
Going for a refurb is probably the easiest option if you don’t want to get into checking individual components yourself.


08/04/10 @ 13:00
Comment from: Ian


Just before I send the board away, is the way of confirming g the electrode by checking continuity between the spade terminal and the body of the electrode?
Or could I check at the electrode pad on the board (where the spade fits) but what type of reading would I be looking at ?



09/04/10 @ 15:49
Comment from: Tony Martin
Tony Martin


Measuring continuity between the electrode tip and the pad on the board should be good enough. While you’re at it check that you have a good earth connection between the board and the metalwork (the green/yellow wire from the board to the earthing stud on the case.
Actually the spark is at sufficiently high voltage that even if you disconnect the electrode it will spark across to the chassis. That’s why the fault finder suggests looking for sparks elsewhere than at the tip of the electrode. In fact you should hear the click of the spark as well as see it if this is happening.
One other thing you can check, if you have the cover removed from the control board: the body of the gas discharge tube labelled SP1 should glow momentarily and repeatedly indicating that the spark generator is working.
Good luck with the refurb.


10/04/10 @ 09:32
Comment from: Irvine

I need to locate the spade terminal on the control board for the spark electrode wire. I have read your notes above, but cannot see a terminal. On the back left of the board I can see a slot where there is a pcb circuit point, is this it and if so I still cannot see how the wire terminal fits?

13/04/10 @ 17:26
Comment from: Richard  

Many thanks Nick,
My 21 year old Netaheat Profile 80E was acting up big time. Pilot light would come on but not the main burner. Thought it might be the main Gas valve (GV2) until I read your comments about the P.C.B. I got the soldering iron out and did a quick check on any possible dry joints. Only spent a few seconds on each suspect joint as I did not want to damage diodes etc. from overheating. Works like new now !!! Again, many thanks. Donation to your charity on the way tonight.

13/04/10 @ 21:01
Comment from:

@Irvine, yes that slot is where the spade connector push-fits in place.

@Richard, many thanks!

13/04/10 @ 22:17
Comment from: Irvine

Thanks - I have plugged the ignotor lead in and the boiler is now firing, so I now have heating.

I recently had all 3 thermostats replaced to sort a long running thermal cut out issue and all seemed well until last week when I noticed that adjusting the main control knob did not have any effect on the temperature in the rads. I re-seated the main control thermostat as it seemed loose in the clip and I also used some high temp copper grease (as used in cars) to help bond it. (The ignitor lead just fell off in this process).
Question: The main control themostat and knob has just been replaced and did seem to work for about 4 weeks, are these suspect to failure so quickly - or is it more likely that the control board itself is now defunct?

The board has been in situ for 6 years, the boiler is 15 years old.

15/04/10 @ 11:28
Comment from:

@Irvine, failure so soon seems unlikely. Having said that, it also seems unlikely that another component on the board would duplicate the effect of a failed stat. More likely is a connection problem - could the copper grease short across the stat connections so it appears to be always on full?

15/04/10 @ 20:03
Comment from: David Joseph
David Joseph

Hi Dr. Nick
My Potterton Profile 40 started playing up last week. It fired up ok but I only got 2 - 8 minutes after which it would cut out but leave the fan still running. There was a sparking sound as it tried to relight. A plumber friend had a look & pressed reset & (as always) it behaved fine while he had his cup of tea only to cut out again after he left.
I found your site, the pics made it understandable what needed to be disconnected etc. - very useful & straightforward. I fired the boiler up with the wiring and pcb exposed & noticed sparking from a bad solder joint, the leftmost pin under the large connector block at the front. Put a bit of solder on the back of the pcb to the offending pin, no arcing, all works 100% now. I’m skint at the mo, but when I get some work I’ll make a donation. Cheers!!

19/04/10 @ 13:42
Comment from:

@David Joseph, glad it helped!

20/04/10 @ 08:46
Comment from: Tony Martin
Tony Martin


Hope I’m not stating the obvious, but you could easily test if the control thermostat is working properly. Just run the boiler at a low setting and, when it is up to temperature and the burner shuts down, turn the control knob up and it should re-light, since you are demanding a higher temperature.
If you had the thermostat removed you could also check operation by dipping the sensor in hot water. The temp range is supposed to be 55 C- 82 C.

21/04/10 @ 11:24
Comment from: Ian

Thank you to Tony Martin and dr-nick for your previous advice. My boiler is now working but a slightly different solution.

See my original post 31/03/10
I managed to buy a replacement board on Ebay for £15 which was described as working. When it arrived there was evidence that it had been previously reworked.
When fitted, the boilert behaved similar to many of the faults described on this forum - fan frequently stop/starting - which is the classic 3 capacitor problem. I changed the 3 capacitors ( with very poor soldering), when put back into the boiler I had the same symptoms as I had with the original board.

Heat demand
Fan runs continuous
Pressure switch activates
But no spark
This then gave me confidence that the board was actually good (the chance of 2 boards showing the same fault).

Also as Tony mentioned SP1 glowed, I used a mains tester on the sparklead pad on the board that showed that there was power there (unknown amount).
Although I was getting continuity to the electrode I decided to change the electrode and HT lead ( total £9) . The boiler worked fine, I have changed the refurbed Ebay board back for the original (Due to the poor soldering that I had done on the Ebay board) and still works fine.

Although I cannot be sure I suspect the HT lead but for £9 and a spare known good board for £15 a happy outcome.

Thanks again for your advice

26/04/10 @ 13:27
Comment from: Steve

My Potterton Profile 50e has a problem this morning, fan runs continuously when switched on, but no pilot light. Found a guaranteed refurb PCB 407677 on ebay for £30, so have ordered and will try fitting myself. CORGI guy I called actually said it’s worth trying before calling him out, which is reassuring. Guide above looks good, will let you know how I get on, cheers.

04/05/10 @ 16:06
Comment from: Steve

Done. Replaced PCB with the refurb one, powered it all up again and Hallelujah, pilot light restarts, heating and HW both on and working.

My comments on replacing the board:
It’s a bit more awkward than I thought it would be, for two main reasons. First is that the larger block connector is really stiff to remove, took me some time with the needle-nose pliers to get it off. Second is that the access to the rear two plastic mounts is really awkward. Took about 5 minutes alone getting those off carefully. Everything else was pretty easy really.

Make sure you have handy before you start:
Large cross-head screwdriver
Small straight-head screwdriver
Needle-nose pliers
Maybe something to clip a cable tie if you’re using a refurb board that comes with the leads bundled together.

Thanks very much to everyone who has contributed to this thread, this has saved me a lot of time and effort. I can recommend the ebay store I got the refurb PCB from as well.
They are called All Spares Direct:


06/05/10 @ 13:27
Comment from:

@Steve and @Ian, thanks for the feedback!

06/05/10 @ 18:59
Comment from: mike pimlott  
mike pimlott

Thanks for a fantastic forum.
I have just fixed my boiler after suffering for nearly a year.
I experienced similar problems encountered by previous posts. The boiler fan running without igniting…..a sharp tap fixed it for a while…then I left the PCB holder hanging down as that seemed to work best as a previous post found.
A couple of days ago whilst the garage was in darkness, I could see arcing from the PCB…..if I touched the 6 pin holder I could make the boiler ignite and stop at will…..I removed the board and found several dry joints.
I re soldered them and put it back together only to find that nothing would work and I could not reproduce the fault.
I decided to replace the 3 capacitors…..then the orange wire came away from the connector, so I had to solder that.
Still it did not work.
I took it all apart and noticed R15 was loose, so I tried to replace that and ended up lifting the track around the holes…..what a nightmare.
I ended up soldering the legs of the resistor on to the nearest pins further down the track……..not a pretty sight.
I tried it once again and it did not work….so I decided to put it all back together and call the plumber, with the intention of replacing the PCB with a new one.

I say put it all back together because I was not putting the cover back on after each thing I did.

Needless to say, as I turned the dial it clicked a couple of times and then roared in to life.

I wish I could say what it was exactly that caused mine to stop but it runs now and cost 79p as opposed to £120.

The board is not a pretty sight but it works.

I hope this helps someone else like this site helped me…..cheers.


06/05/10 @ 21:14
Comment from:

@mike pimlott, glad you’ve got heating again. Since it certainly sounds like the board at fault, you might want to consider a refurb to tidy things up at some stage - should be cheaper than a callout.

07/05/10 @ 08:00
Comment from: Paul Young
Paul Young

Can I also echo my thanks, I’ve learnt a lot about this boiler from your blog.
I have a similar problem ie erratic firing up but I can reliably sort it by opening the front of the boiler which causes the fan to run continuously, leave it 2-3 minutes and shut it and the boiler fires up and stays alight until switched off.

Any ideas ?


16/05/10 @ 18:39
Comment from:

Hi @Paul Young, I’ve no particular ideas, especially since it’s intermittent. The only advice I can reiterate is to work the troubleshooting chart, from powered off. Good luck!

16/05/10 @ 18:56
Comment from: Danny

This a very informative blog…thank you.
To add to all the info here, i would advise …to always check that the front panel of the boiler makes a good seal of the chamber…and that the restrictor in the fan tubes is clean from dirt…the APS won’t switch over if you have problems with either of these…and don’t forget that fans can age and not function enough to perform correctly.

17/05/10 @ 02:03
Comment from: Tony Martin
Tony Martin

Paul Young
It’s not clear from you post which part of the start-up sequence is failing when the boiler doesn’t light:
1. Does the fan run continuously ?
2. if so, does the pressure switch activate after a while (you should hear the gas valve switch) ?
3. Do you then get a spark ?
My guess is that the pressure switch is marginal in switching and your trick of opening and shutting the casing is giving it a nudge sufficient to make it switch. Either that or you have a poor seal around the case front (a small strip of tissue paper will detect any escaping air)
The other thing that occurs to me is that the fan itself might be on its last legs and not able to produce quite enough pressure in the casing

Tony M

17/05/10 @ 15:27
Comment from:

@Paul Young, there you go :) Two useful pointers! Thanks guys.

17/05/10 @ 18:29
Comment from: Irvine  

It’s a few weeks since I used your excellent site and I have since replaced my PCB with a £40 refurb (I was more confident in doing this rather than the soldering approach). This was very easy as I put the PCBs side-by-side and then individually replugged each connection, this took about 20 minutes in all.

I still have a scenario where the main control thermostat does not seem to work. The rads run very hot, adjusting the main control knob makes no difference and does not switch off the boiler until the “physical” click. In all other functions the boiler is now working fine.

3 months ago I had a gas engineer friend replace all three thermostats including the control thermostat. When I replaced the PCB I specifically noticed that the connections to this thermostat used 2 similar white leads.
Question: does it matter which way round these white leads are connected to the thermostat? If it does matter, and if mine are connected wrongly, does this explain my problem?

In addition to the boiler issue, I have recently flushed the pipework systems and replaced some TRVs. I also fitted a MAGNACLEAN filter and can recommend this device as even after flushing, the material collected by the magnaclean was impressive.

Can you once again publish where you wish donations to be sent, your site must have saved £000’s by now.

Thanks once again.

29/05/10 @ 14:32
Comment from: Irvine Webb
Irvine Webb

Hi again
Just to let you know that I have replaced (again) the main control thermostat (£18) and the system now seems fine as I can now adjust the system temerature.
The last thermostat replacement lasted 1 month and since then I have replaced the PCB, but I cannot see how the PCB would damage the thermostat.
Anyway, thats it until next winter!

Read your blog, glad you liked my home town of Stratford-upon Avon.

05/06/10 @ 10:49
Comment from:

@Irvine, thanks for the feedback. To answer your questions, it doesn’t matter which way round the white thermostat leads go, as it’s basically an on-off switch that just happens to be temperature-dependent. Sounds to me like you had a duff one installed. I’d bend your engineer friend’s ear :)

As for donations, if you or any of the other 15,000 viewers of this page have saved money and wish to contribute to my hosting costs, that’d be very welcome! Just click the secure PayPal button above (you don’t need a PayPal account, you can just make a one-off credit/debit card donation). I’m contributing 50% of anything I receive to the NEA charity (details next to the button).

06/06/10 @ 18:25
Comment from: Stan

Found your page via google when I returned home to find that there was no hot water and the Profile 80e wouldn’t fire up.

Noticed some arcing and sparking from underneath the front right hand side of the PCB, whipped it out and found a nasty cracked dry joint.

Fired up the soldering iron and 5 minutes later the boiler was back working and the water was heating.

Thanks for your informative write up, if I do need to change the capactitors do need replacing in the future, I am well up to speed on getting the PCB out for another quick repair.

10/06/10 @ 03:01
Comment from: Kim

Hi, Ref Prima 60F
just another note that might help somebody else.
Reading through the comments, somebody asked the question (could the caps be at fault on a 15 month old pcb) Well the answer is yes and the last thing I expected. Mine was about 16 months old and looked like new inside. No sign of the usual bad joints at the base of the plug socket etc. I replaced all 3 caps, but the faulty one was the axial one (wires come out at either end) C7 22uF. Maplin p/n AT04E They don’t do this in 100v or 103 degC versions so 63V had to do. Anyway when tested, the faulty one measured 4uF rather than 22uF

The problem with the boiler was: On fire up, it would run the fan for 5 sec then stop then run 5 sec again between 4 or 10 times before firing. It would never try to spark. Basically I guess it needs a few seconds more than 5 to allow enough diff pressure to pull the Air Press SW in

I carried out the flame safety test procedures shown in the manual after reinstalling the pcb and I would recommend this to others.

Given the application and location of the pcb, I have never seen such poor build quality. It is basically designed to fail after a couple of years max.

Regards Kim

02/07/10 @ 20:48
Comment from:

@Kim, thanks for the tip, certainly agree on the design!

02/07/10 @ 22:28
Comment from: Simon Carus-Wilson
Simon Carus-Wilson

39p spent at Maplins and my Potterton Prima F 60 is purring like a kitten.

Thank you so much.

All the best Simon

26/07/10 @ 13:42
Comment from: Emm


Great blog btw. Does anyone know where I can get an outer casing from for one of these boilers?

20/09/10 @ 13:44
Comment from:

@Emm, no idea I’m afraid! Thanks, Nick

20/09/10 @ 21:22
Comment from: Robro

Hi Dr. Nick,

I suspect the overheat thermostat on my Suprima 80L is faulty so have bought a replacement which I have yet to fit. The boiler can run for several days or only several hours before the system locks out . The reset button usually fires up the boiler first time but very occasionally takes two or three attempts before the boiler ignites.
Could you please advise if it is necessary to install the new stat with any kind of grease to increase temperature transmission or is it straight replacement.

Thank you

14/10/10 @ 14:17
Comment from:

@Robro, Hi, I have no experience with changing the stat, so can’t really advise I’m afraid. Have you looked at the installation guide (link near top of article)?

15/10/10 @ 09:20
Comment from: ged easter
ged easter

most helpful diagnostic site I have come across as i battle to solve prbolem with my potterton profile 100e boiler. When heating or hw is called for boiler does not fire up. When re-set button is pushed it fires up and both water and heating ok. After a while it shuts down and doesnt fire up. This morning called for heating ONLY and after pushing reset button the heating is going fine. It seems that when HW AND CH is on it shuts down when HW has been heated. So far have had the fan replaced. HELP!

17/10/10 @ 14:13
Comment from:

@ged, sounds odd - all the boiler sees is water in the circuit, it doesn’t know what it’s for. My guess would be that it’s overheating when both are on just because it’s spending more time on. Have a look at the troubleshooting guide in the installation manual and see what it says about overheating for starters.

17/10/10 @ 16:37
Comment from: ged easter  
ged easter

Many thanks for your quick response Dr Nick.
The boiler has since shut down so your explanation is spot on. From the fault finding chart in my user guide, if I have read it correctly, it looks like the ‘over-run thermostat’ or ‘overheat thermostat’ is faulty if they are the same thing. From all the previous posts this probably does not need a ‘gas safe’ registered chap to install. Is it easy to install - I am no diy expert!

17/10/10 @ 16:53
Comment from:

@ged, they’re two separate stats. The overheat stat detects if the water is getting too hot and, if so, trips the boiler to protect from danger. In pumped systems, the overrun stat ensures that the pump keeps running a little longer after the boiler stops firing, so that the water keeps flowing and so naturally cools off a bit - otherwise the residual heat left in the boiler could continue heating the water left in it, up to a temperature that trips the overheat stat.

I’ve only fixed one specific PCB fault on my boiler, so have no experience of stat problems. I hope you appreciate that I can’t, in good conscience, offer advice on the wisdom of DIY repair. If in doubt, play safe. At least you’re armed with the information to guide a professional to an appropriate repair at minimal cost.

17/10/10 @ 17:38
Comment from: ged easter
ged easter

Dr Nick, thanks for very useful clear comments. I will get onto my trusted gas register man and update you if and when my problem is solved.

17/10/10 @ 18:33
Comment from: george cosgrave  
george cosgrave

PrimaF50 dead tried reset button, no go.
No mains at timer control across points 2,4
Any suggestions ???
Have spare PCB that looks ok will i fit and check response ???

18/10/10 @ 11:52
Comment from:

@george, sorry, no idea. I know what I know about my boiler, but I’m afraid I’m not a diagnostician for all possible faults!

19/10/10 @ 08:40
Comment from: Tom

Just to say many thanks for the advice given on this site. Our Profile 50 stopped working yesterday brrr…. Fan runs but burners won’t light. Removed PCB and replaced electrolytic capacitors as you advised and resoldered some joints on the PCB, especially under one of the connectors, which looked ‘dry’. R15 looked like it had been distressed as well with some of the markings burnt off, so replaced that as well - used 2W 100Ohm, fits if you bend the legs a bit. Reinstalled the PCB and now works perfectly. Components cost around a quid. Not sure if it was the capacitors or dry joints causing the fault, but after the effort taken to remove the PCB, it seems sensible to replace the capacitors anyway, just in case.
Happy to make a donation considering the considerable amount of money you have saved me. Many thanks.


21/10/10 @ 23:42
Comment from: Tim S  
Tim S

I have a Potterton (Read: SATAN) Boiler - the Prima 40f. Same main PCB as the article. Mine does this:

0. Fan Starts and remains on constantly throughout
1. Spark
2. Pilot Light Ignition
3. Main burner ignition
4. After 0-3mins main burner shuts off, pilot remains lit (and always is)
5. Goto 3

I’ve got voltage to GV2 (not that this in itself means the solenoid is working correctly). Having just stumbled on this GOLDMINE of amazingness i’ve bought 3 caps and the resistor and will investigate my PCB this weekend to see what’s broken. Worst case, i’m going to put some new stuff on the PCB for a couple of quid, best case is i’ve got a PCB problem and I can once again heat my house.

Because my main burner comes on a ‘bit’ I can eventually get hot water but CH is def. a no-no. Obviously something is on the way out and my symptoms suggest the fan, APS and ignition sequence are OK.

Big up to Dr Nick, beer money on the way if this works!

29/10/10 @ 15:00
Comment from: Tim S
Tim S

Update on my problem - it’s fixed!

Just did the capacitors - and low and behold it’s running perfectly!!! Many thanks :)

03/11/10 @ 09:59
Comment from:

@Tim S, good news!

03/11/10 @ 22:47
Comment from: Kam

Excellent write up! Like you say, although with enough googling one can find the information scattered in forums, nobody else has bothered to do a write up - so two thumbs up to your effort in putting together a guide!

My Potterton Netaheat Profile 60 (20 years old) conked out for the nth time again last night and I instinctively knew it was the board, as it’s pretty much always been the culprit. Adamant not to splosh out for another board, I was determined to find whether it was likely to JUST be the electro caps. Every previous occasion that it’s broke I’ve been too busy at work but this time I happened to be at home and, hehe, I was either gonna do the cheapo fix or bin the damn thing for an up to date Vaillant! Anyway, back up and running - and good job it wasn’t that cold last night.

There is one thing make other readers wary of: when desoldering (regardless of whether using a solder sucker/pump or not) it’s possible to damage or destroy the pad linking the component to the track(s). The quality of the board is simply RUBBISH! My desoldering pump, literally, sucked the pad off the board! I had to make an improvised track repair - click to see pic.

Again, good write up and for helping out many people with the same problem. Speaking personally, I’ll probably replace mine the next time it breaks - time to update/upgrade to something significantly more efficient and quieter!

09/11/10 @ 12:10
Comment from:

Thanks @Kam!

09/11/10 @ 12:50
Comment from: Kam

As an addendum, while it is important to use the fault diagnosis chart (p.32 in the installation and service manual) it isn’t guaranteed to be correct. After the capacitor swap my Profile 60 would fan on (continuous), spark but no pilot. According to the diagnostic chart this indicates blocked pilot jet or suspect GV1 valve. In reality, it was actually bad contact on the main connector block of the board.

I had visually checked the board for any dry joints and reflowed any pads that looked suspect - most looked sound. Obviously, this was not the case as it conked out again after a couple hours’ use. I really thought that I had a gas side problem until I touched the connector block and the thing fired up. To verify that it wasn’t just coincidence I waited until it wouldn’t fire and repeated the connector wiggle. To my dismay, it didn’t illicit a firing so I resigned to having get a CORGI mate in. Couple minutes later, I tapped the connector and it fired up. I was then positive that it was still a board problem. Although the symptoms manifested as blocked jet or dodgy solenoid/valve, it was bad/intermittent contact at the board connector pins for controlling the pilot valve.

The lesson to take away from this is that
i. you should still use the diagnostic chart
ii. you should still use your brain and logical deduction
iii you should use repeated and methodical testing (however rudimentary) to eliminate coincidence

I removed the board and reflowed all of the joints. In the process, I managed to break the HT spark lead connector so had to recrimp - looking for a suitable crimp actually took longer than anything else! I don’t to jinx it but I’ve had the system on for twelve hours now and it’s still working. This time, I’ve not replaced the cover and reassembled the cupboard - just in case it does conk out again. A couple more days stress testing should be sufficient reassurance.

10/11/10 @ 23:01
Comment from:

@Kam, thanks, that’s useful feedback. Glad it’s working better now. I guess I’d only comment that people do need to start with the chart, from the beginning, as it gives you a logical framework. When these boilers go wrong, there can clearly be a number of reasons, and if you’re not an expert, you can risk going up a blind alley if you guess at the cause first. From some previous comments, I think that a few readers may have jumped to a solution for a problem they haven’t actually had.

11/11/10 @ 07:41
Comment from: mike  

hope u can help we have the same problem as most others on here the boiler does it cycle fan runs aps clicks and doesn’t fire keeps doing the cycle till it fires can be 30 seconds to 30 mins , but we are on the 3rd pcb first lasted 7 years next 13 months present 18 months is there any reason why this keeps happening . we had the boiler enclosed in a cupboard when the kitchen was refitted but it has the top and bottom cut out so the air can follow around the boiler so it doesn’t over heat , but i’m wondering now if the boiler is getting too warm and this is why the pcb is cooking , i have the no 2 pcb in front of me and the circuit board is looks perfect no bad connections or burns on resistors etc
? ,i don’t want to have to spend on other pcb for the same thing to happen again , i’m wondering if its worth replacing the capacitors as listed in this thread , is there any way of testing them on the board to see if i can find which one it is
regards mike

11/11/10 @ 11:15
Comment from:

@mike, for the cost and effort to resolder three caps, I’d take the punt myself, but I’m a confident solderer. Note that failed electrolytic caps won’t necessarily show visible symptoms. I guess you could try a capacitance meter across them in situ if you have one. If not though, it’ll be cheaper to buy the new caps and be done with it! Good luck.

12/11/10 @ 19:53
Comment from: mike

hi nick
update on my problem !
replaced the three caps 1@22uf and 2@100uf , its made no change , when the boiler fires from cold it lights first time every time , if the boiler is run on a low setting it refires every time 1st time, when its turned up 5 and above which we have to use for the reheat time on the hot water tank in the mornings it fails when the boiler is hot and won’t complete the cycle which you can hear it go though until the boiler cools down . I’ve check the fan and it seems to be running at right speed with a good pressure , i’ve check the pressure pipes are clear the aps switch’s over fine and I’ve tested this also with a meter, when i take the high pressure pipe off the aps the fan runs continual and when pipe reconnected the relay in the pcb clicks and it runs ok again , so its as if the boiler will not relight / complete the cycle to light until its cooler right down any ideas , i’m beginning to think this has only started playing up since the boiler temperature was turned up, i don’t want to get some one out who is just going to put every part on until the problem is sorted as we had this a few years ago with a car , the main dealer put an ecu on at a crazy price and two days later it did the same thing and the local garage to where it had broken down put a 5 quid relay on and it never happen again
regards mike

15/11/10 @ 09:12
Comment from:

@mike, shame it’s not fixed it. You hadn’t mentioned that it was 100% reliable from cold. If there’s a difference between hot and cold operation it’s more probably a thermostat problem surely? Probably the overheat stat, or possibly the gravity-control/pump overrun stat (depending on your system type). Have a look at the right hand side of the troubleshooting chart, see if that fits the symptom when hot. Details of the different stats are in the manual too. Best, Nick

15/11/10 @ 20:57
Comment from: Richard D
Richard D

Hi, I tried your site most impressed.
My fault is with the 100e,
Fan Starts.
pilot light comes on
Sprk continues and main gas valve does not come on.

I thought, faulty PCB, as an electronic engineer no probs changing the capacitors, R15 also dry joint.
In fact dry joints everywhere. Re soldered, refitted same problem.
Air pressure switch works as otherwise wouldn’t get pilot ( Is this correct?) It does switch mechanically when you blow across the inlet ( not directly in).

So followed fault chart, and since I found several faults on the board, I thought buy a brand new one.
Confident armed with credit card…..
Fitted it ….. Same problem.

Any ideas, I’m pulling what little hair I have out?

I metered out the coils on the gas valve both were approx 900 ohms. The spark continuing is what gets me.
Clearly the relay has to switch over so the EV2 valve gets a Neutral, and the high voltage spark stops.
The solenoid does not get a neutral, so the fault is not with the gas valve! All wiring checked for continuity.
Is there something else that must happen?

Could it be a temperature sensor. We operate it as fully pumped.

18/11/10 @ 22:49
Comment from:

@Richard D, I don’t know the answer, as it’s not the fault I had on my boiler, but from the chart, I agree that the air pressure switch sounds OK. My intuition is that it’s something in the gas valve, especially if you’ve swapped the board already. I don’t think the thermostats can be relevant if the main burner is trying, but failing, to light.

Maybe you’ve just not got enough gas flowing through the pilot? If the spark doesn’t stop, the chart suggests the two tests above the chart: flame supervision using the pilot screw (as mentioned in §4.3A on p26) and flame current. If (big if) I read it correctly, there needs to be at least enough pilot gas flow to permit a 1.5uA current through the flame and spark electrode, which commands the PCB to shut off the spark and open the GV2 (main burner) valve.

If it is a fault with gasworks, I’d recommend you get a certified pro in and point them at the relevant bits. Good luck, and let me know how it goes!

18/11/10 @ 23:58
Comment from: Richard D
Richard D

Hi, it was exactly that, I predicted the pilot light, but I could not touch any Gas pipes, I called in a Gas safe engineer, and said I’ve got a blocked pilot jet, strip it and re-assemble it please. He was most impressed.

He did exactly that.
We now have a working boiler.
So if any of the readers have a similar problem, where the pilot is lit and it is still sparking, it is because the pilot flame is too small, not allowing Gas ionisation to occur.
The control box passes a current through the flame, and the current changes when there is a good flame before the main burner can kick in.
I wondered how the boiler knew if the pilot is lit without using the normal thermocouple.
I’m still pleased that I changed the controller, I suspect the old one still works, but the timing must be way out, 2 of the 3 capacitors measured a quarter of their value.
Dry joints every where. (Old board in the cupboard just in case)
Thanks again.
Best regards and thanks,
Richard D

19/11/10 @ 17:25
Comment from:

@Richard D, great!

19/11/10 @ 20:37
Comment from: mike fraser  
mike fraser

well done mate after reading all these stories i guessed i had the same problem so on to good old ebay for a 407677 pcb when i removed the old one i noticed like many others have mentioned that r15 was burnt and z3 had dry joints at both ends after replacing the board and switching on the boiler , (watch out for this happening) nothing happened for about 45secs then boiler fired up i suspect the delay was the new board had no charge in the capacitors however it gave me a scare thinking now it is worse then it was before so for people changing board dont panic if nothing works rightaway we are now 24hrs on and the boiler is firing up first time every time and faster then when it was new so if you have the same problem go for it and save yourself around £350 for repairs please beware when soldering the track is not great

05/12/10 @ 09:31
Comment from: john  

Help , My Potterton Profile 50 has stopped and will not start, power going to pump and diverter valve, the fan runs continuos but no spark, of the 3 wires on air pressure switch only brown and white have power to them orange is dead, does this mean switch is broke or could it be the electronic control.
I have blown into Pressure switch and can here a click.
Had quote for £4000 from BG to replace boiler but this is way out of my price range so am trying to fix old one with your help

17/12/10 @ 06:07
Comment from:

@john, sorry, it’s not the problem I had with my boiler, as your fan isn’t cycling. I don’t know how a working air pressure switch is supposed to react. From fig.27 of the installation guide, it describes terminal 2 (orange) as NO - whilst the other two (white and brown) are NC and C respectively. Do you think it’s a reasonable guess that C is common, NC is normally closed and NO is normally open? If so, I’d expect the latter two would be in circuit whilst the orange isn’t, much as you describe. That’s pure speculation though.

I’ve nothing else useful to suggest apart from to work the troubleshooting chart. In the Is electrode sparking? column, there’s a sequence of things to try in order. Based on your description I’d be suspicious of things above the pressure switch. Good luck!

17/12/10 @ 15:10
Comment from: brian

i just wanted to leave a post to thank you for all the information. having had a problem last year with our boiler, it is serviced every year,so when it stopped we were disapointed to say the least,and on the first day of a bad cold spell!!We seeked help from our next door neighbour ( plumber) who replaced the air pressure switch, it worked ( but we left on constantly just incasse it didnt start)!! All well until this year until just before the Christmas the cold spell arrived and the boiler stopped again! Neighbour called again but obviously didnt need to replace air pressure switch again, so eventually he got it going by blowing on the air pressure tube! again we left it on consatantly as he did not really fix problem. a search on the web and found your blog and reading all the post and following your directions, my boiler is now working better than before! I have a 100% better understaning of the workings of my boiler ( obviously i didnt go near gas components ). the pcb was made in 1990,
so im hoping with the replacment caps it should go on for a few more years. One point to other people trying this fix. when i replaced everything the boiler did not work straight away, for whatever reason it just went through the start up cycle but would not start. so feeling very deflated i tryed the air pressure swith again and it fired up and has worked faultless since. Anyway thanks again for all the advice you saved me alot of money. cheers brian

08/01/11 @ 15:48
Comment from: al j
al j


just done what you said on this page,boiler firuing up 1st time. the last 12months its been whirr click, repeat about 10-15 times then it would fire up.

many thanks for the pics they helped.

maplins charged me 97p for the 3 capacitors but i can live with the dearer price, theres a recession going on, lol

all the best

16/01/11 @ 13:23
Simon Wells

I stumbled across this blog and found that the 22uF radial was only ready 4uF.
Tip to maplins and bought the last one they had, but it has not resolved the issue for me.

The fans still turns then stops.

Have replaced the air sensor, check pipes for leaks/cracks etc.

Think I might have to get a new board, do you know where to get them from?


PS, Its great to see a blog post helping out so many.

08/02/11 @ 23:34
Comment from:

@simon, I’ve seen them in the past on eBay. Google 407677 and see what you find.

09/02/11 @ 07:22
Comment from: Dave Love
Dave Love

Excellent site. I fixed my Potterton 407677 exactly as you described. It cost under 1 pound.

10/02/11 @ 12:52
Comment from: Graeme

Fantastic, I am now feeling the warmth come through my radiators as I type.
Re soldered a few dry joints and away I go.
Thanks so much for putting info online as it has obviously helped so many folks that have the badly flawed potterton pcb boilers. Cheers again.

12/02/11 @ 14:58
Comment from: Mister P  
Mister P

Hi there I fixed my 50F bolier 2 years ago when it was cycling on and off, and the replacement capacitors worked a treat. But for the last month have had an intermittent problem of the boiler not starting first thing in the morning - can hear it coming on (not sure if its the fan coming on) but no attempt to ignite - although its not cycling as before. Switched it off at the mains & than back on and it started fine. Now this morning its refusing to start despite turning off and on - I know i should have looked at it ealier :-(
Was thinking of just getting a recon PCB this time - but not convinced it is the PCB - any ideas ??

20/02/11 @ 11:41
Comment from:

@Mister P, the fan sounds like a quiet whirring sound; should be quite distinct from the clicking of the spark at the electrode. If it’s not sparking then it could be a number of things - the troubleshooting chart gives you some things to look at in order. Good luck!

20/02/11 @ 15:57
Comment from: Mister P  
Mister P

Yes got a copy of the troubleshooting guide and it points to the air pressure switch (fan is running OK) - I think it will have to be a Corgi man on that one.

20/02/11 @ 17:07
Comment from: Neil  

I have a Potterton 60, which uses 407677. My boiler will light, but then go off and not come back on. The fan does not cycle without the boiler lighting. If you give the bottom of the boiler a whack, the fan comes on and then it lights…….until the next time. The fact that it comes on with a tap suggested a bad connection somewhere, but I’ve had the board out, replaced the electrolytic caps and resoldered all the joints (some of which parted like the Red Sea as soon as the hot iron came near). No improvement. The area around each Zenner teminal is a teeny bit discoloured……but maybe there is a fault somewhere else?

28/02/11 @ 21:53
Comment from: Paul

I have a profile 80e about 16 years old. It was playing up with the fan starting and taking about 10 goes to start up. I thought it was sludge or something. I cleaned the system hoping that would clear it but it finally gave up the ghost last friday night. I thought a new boiler would be needed since it was a w/end and no plumbers. I checked the fault finding guide on the installation instructions. They pinpointed the controller pcb. At £120 it was an expensive quick fix, since I was thinking of changing the boiler anyway. luckily I came across your site, so Monday bought the capacitors from Maplin £1.01! The boiler started straightaway. I saw sp1 sparking as mentioned in earlier posts. This is a neon spark gap to protect the pulse transformer for the ignitor.So it shows that the ignitor system is working at least.
Great advice and got us in hot water!

11/03/11 @ 20:32
Comment from: Phil

another dead f40 revived for less tan a price of a pint thank

07/04/11 @ 21:01
Comment from: hamish

Hi. Have had a lot of trouble with potterton profile 50el boiler. Came across your website and went to Maplins for the three capacitors and job done, works 1st time. Thanks very much for your info saved lots of money.

16/04/11 @ 05:47
Comment from: steve

Anyone know the value/spec.ytpe for diode (?) Z2 on the 407677 PCB?

Clusy me managed to crack the glass outer whilst levering the covers off the relays for contact inspection

25/05/11 @ 12:07
Comment from: simon

I am a Gas Safe registered engineer and I have to say that this DIY approach to gas work is DANGEROUS. Some comments on here like checking the gas with a match defy common sense and the law in equal measure.

There are other faults that can cause similar symptoms to the ones mentioned.

Gas regulations clearly state that any person doing work on any gas appliance must be competent to do so. The only way you can legally be competent is to be Gas Safe registered.

I humbly suggest that if you have a problem with your boiler you should have it fixed by a Gas Safe engineer and have it checked regularly to make sure it is safe.

If the safety of you and those around you is not worth the price of getting in a qualified professional to do it legally then carry on.

19/06/11 @ 21:19
Comment from:

Happy to publish your comment Simon. I agree entirely. No-one who is not Gas Safe registered should fiddle with their gas fittings - I have expressed this clearly in the original article and I’ve repeated it many times in replies to commenters.

I have de-published one comment by a DIYer who mentioned using a match. He wasn’t “checking the gas” but better safe than sorry. The only other relevant comment refers to a smoke match for testing the case seal, which is quoted comment which appears to have been professional practice of a CH engineer some 20 months ago. Maybe his practice is not perfect. I’m not endorsing it either way.

The Gas Safety (Installation and Use) Regulations 1998 are intended to ensure that incompetent people don’t work with gas fittings. Entirely sensible legislation which undoubtedly saves lives. Section 2 defines “work” as:

(a)installing or re-connecting the fitting;
(b)maintaining, servicing, permanently adjusting, disconnecting, repairing, altering or renewing the fitting or purging it of air or gas;
©where the fitting is not readily movable, changing its position; and
(d)removing the fitting;
but the expression does not include the connection or disconnection of a bayonet fitting or other self-sealing connector.

The circuit board is removable without opening the case, by disconnecting push-fit connectors. Its replacement has no effect on any pipework, valves, regulators, storage vessels, flues or other fitting designed for the purpose of effecting a gas tight seal in a pipe or other gasway. I therefore don’t believe that repairing this circuit board constitutes gas “work". I’m content that my actions did not compromise anyone’s safety. I’m satisfied with my electrical competence. Gas is another matter, and that’s why I use my local Gas Safe engineer when I’ve a problem with gas. I advise (and this is the extent of my advice on gas) others to do the same.

19/06/11 @ 23:30