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.


by Nick  

I'm going to post three separate entries tonight. Three different topics, which I figure deserve their own separate space.

Firstly, my back is on the mend. The valium kicked in on Monday night. After going to sleep at 10.30pm, I stirred several times in the night. Each time, the same sensation of literally being drugged: it felt like I was wearing a suit of armour - a powerful combination of lethargy, feeling tied-down and dispossessed. I thought about trying to roll over, but it didn't feel worth trying, and it didn't feel like it was my body anyway. Very strange.

I woke up around 7ish, whilst Ros was getting Jess breakfasted, and came downstairs. I managed some muesli, and went back to bed. I woke up again at 11, and threw up. Then back to sleep, only waking for a few minutes more praying to the porcelain god at 1pm and 3.30pm. Finally I got up at 4.30pm, after a total of 18 hours asleep. Rather like the mother of all hangovers, all told. I conclude that diazepam and I don't make good bedfellows.

Did it fix my back? Yes and no. Again, the muscle spasm was gone, but I was left with a constant pain all down my left leg. The physio says that this is my sciatic nerve responding differently as it recovers. Whatever - I've had the pain there constantly since then, although mercifully with a trend of decreasing intensity (dinner-time today excepted). I suppose different is good...

Back to the future

by Nick  

Oh pants. My back is hurting again. I went to physio on Thursday and after manipulation, it was pretty sore all day. On Friday, it got so sore that even after trying to work standing up, I had to leave work early.

After a weekend with no real change, it was still sore this morning. After trying some Pilates and a hot shower, I decided I'd be better off working from home than facing an uncomfortable commute. After an hour of that, I can't walk properly with the shooting pains down my leg, so I've decided to cut my losses and get on the Valium again to try to stop the muscle spasm. I expect that'll knock me out shortly, so I'm going to write a quick blog entry, otherwise that'll slip yet again.

Q. what do you call an 83cm tall, stroppy little girl?
A. Jessica.

She's been a bit of a madam this week. Luckily, we have found that she already has a sticker habit, which can be used for bribery. We think she's teething again, although there's only back molars to come, and no sign of anything breaking through yet. However, the symptoms of grumpiness and a very runny nose have returned. Ros says that Jessie's very much like me when she's grumpy. I don't know what she means. Harrumph.

On Saturday night, she wouldn't settle to bed. After going down at 7.30pm, she kept on waking up until around 10.30 when Ros went and laid with her. After a couple more hours hair-pulling and dozing, I took over, taking Jess to the back bedroom to sleep from 1.30am onwards. Not much fun.

Amusing comments over the weekend:

  1. Giving book to Ros and saying Read it!
  2. Climbing up the bookshelf and, when being told off, saying Naughty books!
  3. While I was fetching pudding after dinner, her calling out Mummy, mmnhm bnhnmn nhnmhm cake; OK?

Hard not to laugh really. Here are some photos. Then I suspect the meds will kick in and I'll be for the living dead treatment... wish me luck.

Hooray for Mummy! I like stickers (even from apples)
A woman's housework is never done Wheeee!
Naughty books!


by Nick  

In other news, I have been hot under the collar about ID cards, and more specifically the latest story about proposals for their mechanism for introduction. Interesting arguments on the site (which I joined in on!)

A leaked government memo describes possible invidious approaches to soften up the country for ID cards. They appear to consider targeting the young to be a good option. These guys ought to run tobacco companies...

Seriously, I really dislike the idea of coercion by stealth. As a liberal, I take the view that you should let people be free to be honest, and deal with it effectively when they're not.

Here's hoping that I don't get a 5am wake-up from the rozzers for expressing that particular viewpoint...

Today's new word is...

by Nick  


It's a bit scary to me, as a child of the '70s, that Jess, who is not yet two years old can not only open DVD cases and remove the discs (before dropping them on the floor), but now knows what they're called too. It came out while she was watching Blue Peter today, where their appeal for unwanted optical media aka Disc Drive was on.

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