Wed Dec 13th 2006 23:38:33: Potterton Suprima Boiler

Right I'm bored, so I thought I'd publish what I learnt when my boiler went wrong a couple of weeks ago...

I have a Potterton Suprima 60 Boiler and it seems they have a terrible reputation for reliability. Just search on Google for "potterton suprima lock out" and you'll see what I mean. The symptom that is mostly seen is the boiler going into reset mode randomly. There can be many things that cause this, however one of the main ones seems to be poor pcb reliabilty. When I removed the PCB out of my boiler I found dozens of blatantly dry joints (look for cracks in the solder, especially around the big pins of the connectors).

Anyway that is the general problem with this product, however it wasn't the problem I had! My problem was that the boiler would work fine from cold and would remain that way for at least 10 minutes (yay hot water!). Then it would start making an electrical hum (like you'd hear from a large transformer). This would gradually get louder and louder and eventually it was making a horrible rattling noise. The boiler would then cut out. It would try to relight 3 times (with varying levels of success), however it would always end up giving up and require me to press the reset button.

The first thing I did was "recondition" all the dodgy looking solder joints on the PCB and replace the Littlefuse MOV which looked like it had been getting hot. Sadly that didn't fix the problem. I then checked all the peripherals. From various forums on the web I found out the following:

  • Heat Sensor - 1 Meg Ohm Resistance
  • Overheat Sensor - This is a standard thermal cutout thing and it should have a resistance of 0 to 2 ohms. Mine measured 1.3 Ohms.
  • Lighter / Flame Sensor - The same thing does both jobs and basically you should check that it's not clogged with soot and has a gap of about 4mm (see the manual)
  • Gas Valve Solenoid - Resistance of about 2kOhms. The valve is actually two valves in one and each valve has it's own coil. This is why there are 5 pins on the valve - 4 for coils (which are connected in series by the wiring loom back to the PCB) and 1 for an earth. When the valve is disconnected from the PCB you should see 300V DC (yes... the AC voltage is rectified by the PCB) between the black and red wires. When you connect the valve you should see about 230V DC (I saw 207V DC). I guess the voltage measurement will vary depending on how your multimeter interprets the voltage which is not AC and not really DC either!

These all checked out so I was a bit stumped. I then noticed that the windings on the Gas Valve were getting really hot (much much hotter than the surroundings). Therefore when my plumber visited a few days later I asked him to replace the Valve with one I purchased from Make sure you shop around if you are buying a new valve - I found prices ranged from £30 on Ebay to £100 from to £160 at my local boiler spares place! Sadly I couldn't get it off Ebay as I needed it the next day so I had it for when the plumber was coming!

Since the valve has been replaced the boiler has been working perfectly again. My guess is that the insulation in windings was dodgy, and started shorting when energised. Hence a low voltage resistance measurement did not pick up the problem. Replacing the valve was pretty easy, however I would recommend getting a plumber to do it as a) it's the law (!!) and b) you need to adjust the burner pressure which is a screw on the valve itself which requires a U-bend thingy. Also the plumber can check you've not got a gas leak once the new valve is fitted by testing at the meter with the U-bend thingy.

If you think your PCB is dodgy, however don't feel happy to repair it yourself, then check Ebay for reconditioned ones or pay a visit to CET ltd. Their business is part exchanging duff PCB's with reconditioned ones. I understand replacement PCB's from potterton have been redesigned and will set you back a few hundred pounds. Apparently Potterton deny they have a reliability problem with their PCB's and will tell you that you are the first person to call them about it.

My thanks to the poeple on the uk.d-i-y group for their advice! If anyone has any experiences or comments on this subject, feel free to email me or leave a comment below.

UPDATE 6/2/07: My parents rang me tonight to tell me to turn the TV on quick - BBC Watchdog were doing a piece about how unreliable Poterton Suprima Boiler PCB's are and how Potterton refuse to accept there is a problem with them. So much of their piece rang true from my experiences that it was scary!!


I would just like to get the terminology right - The U bend thingy's proper name is a water manometer. These electronic engineers!!!

Comment by withheld for personal reasons at 1:01 on Thu 14 December 2006

Great stuff I have a Potterton and it's not gone wrong yet!

I was surfing just in case, thanks for all the info will be a great help one day.

Comment by Olly at 11:48 on Wed 3 January 2007

The gas valve resistance should be about 4k ohms, I have had a similar problem in the past, with the lowered resistance the coil gets hot and in the case I experienced was triping out the RCD on the consumer unit after 2-3 minutes of operation

Comment by Dan at 23:20 on Mon 5 March 2007

Yup, I've just had to fork out for a new PCB for the same boiler - they are indeed rubbish. Thanks for this, at least I know the plumber isn't just spinning me a yarn about it needing replacing.

Comment by Stuart at 13:06 on Tue 15 May 2007

Potterton have actually admitted fault now, and if you go to the BBC website and do a search for Potterton they've a standard letter template that you can send to the CEO, and they're giving refunds for work carried out etc. Albeit I spent over £300.00 and only got £100.00 back, which I am contesting. Good luck

Comment by Ben Stakes at 11:10 on Fri 25 May 2007

I wrote to Potterton using the standard BBC letter - within 48 hours I had a reply back saying they won't pay anything towards it because my boiler is more than 5 years old and "it's not always as clearcut as it may seem" when the PCB fails. There's a mild insinuation that they'll be more interested if I can produce the service records for the last 3 years and they've very kindly offered me a free 1 yr's warranty (the new PCB came with 2 yrs anyway!!). I am going to write back and ask how whether the boiler's been serviced or not contributes to the soldering falling apart inside.

Comment by Stuart at 15:24 on Fri 8 June 2007

Thanks guys. I have just encountered a problem with mine. The engineer is busy reading your comments !

Comment by Joan at 14:12 on Fri 29 June 2007

same lock out probs now hopfully fixed thanks to an hour spent checking then re soildering 18 dry joints.....i also came across a little nugget of info that "poterton have changed the type of soilder so it contains less lead "that means that its not so harmfull and so on but reduce the amount of lead in soilder and does that not make it harder so more brittle and prone to cracking

Comment by ANDY at 21:33 on Fri 28 September 2007

Very helpful to read this. I have 2 Potterton Suprima 100 boilers, interconnected. Both are working but the fan does not cut out when it switches off which sometimes means it wont start up next time. Potterton are so far offering no help other than expensive engineers. Will try the BBC Watchdog letter but from comments above feel pessimistic as they are 7 years old. Strangely Which seems unaware of the problem and I am contacting them to spread the word. Thanks for your help.

Comment by felicity at 10:22 on Thu 13 November 2008

Replaced mine and not had any bother since. It's obvoius the older modle was a design fault. Just ask any Brittish Gas Eng. They qickly redesigned the placement of the PCB.

Must say it's ran perfectly for 8 years otherwise.

Comment by Mike Brown at 13:30 on Fri 14 November 2008

I am at my wits end with my Potterton boiler. In April 2006 I called an engineer out because the boiler kept cutting in and out with increasing frequency. He couldn't find the fault and advised me to call out Potterton. I did for a £260 fee and they fixed it by replacing the whole 'board' (presumably the PCB people are talking about. The Potterton engineer said he couldn't find the exact fault.

Now it seems a similar fault with the boiler has returned. It has begun to refuse to fire without constantly being reset. And it will only fire after being reset if both the central heating and hot water are both set to 'on'. It won't work on 'timed'. Should I just get the whole boiler replaced with a completely new 'non-Potterton' boiler or should I mess about with getting it repaired again and then getting it insured? Any advise? I would not attempt to do anything with the boiler myself so will have to pay someone.

Comment by K Parker at 23:14 on Sun 23 November 2008

Sounds like the PCB has a dry joint on it. Simple to fix if you are an electronic engineer like me (I've fixed my friend's boiler twice now!), however I can imagine it's a bit more complicated if soldering isn't your thing.

I believe there are now improved PCBs available from Potterton that overcome this problem, however that will come at a price. Otherwise buy a new PCB from CET and ask a plumber to fit it for you. I think both those options will be cheaper than a new boiler!

Comment by Gary at 23:20 on Sun 23 November 2008

(I've fixed my friend's boiler twice now!).

LOL. Can't be all that simple if you've had to do it twice!!!

I've just bought a new house with a Potterton Suprima. Having this lockout problem every now and again. I'll take the PCB out and check. Any instructions for setting the water pressure?

Comment by scotty (not so) 2 hotty at 18:07 on Sat 29 November 2008

Hi Scotty,

There was over a year between each fix which I recon is fair enough ;-)

The main joints that go dodgy are the ones to the big connector pins. Obviously check all over however!

No idea about setting the water pressure. I know there is a gas pressure adjuster on the gas valve, however that's probably not much help!


Comment by Gary at 23:18 on Mon 1 December 2008

My Suprima 60 has just packed up and so by reading comments here I ordered a new PCB kit from my local plumbing shop. I have checked the BBC Watchdog and I cannot get a copy of the standard letter template . I was wondering if anyone has a copy so that I can try and get a refund from Potterton.

Comment by Dan at 22:01 on Fri 6 February 2009

I have had the same problem with my potterton boiler and have had a new pcb fitted by my plumber who directed me to the watchdog website but the standard letter is not available now. Does anyone have a copy of that standard template letter please?

Comment by Jane at 8:36 on Mon 9 February 2009

I had this problem and bought a replacement from CET which worked well for a couple of years but this has now developed the same fault. Not wanting to spend another £50 in these hard times I bought an electronic timer from Maplin (MK111 -£5.99) and connected the output relay across the reset switch. (This ensures complete electrical isolation between timer and boiler PCB) You can adjust the "on time" to about 0.5 second which is roughly equivalent to pressing the reset switch. I had to modify the timer to short the reset switch once an hour as its max interval is 1 minute. If the boiler is "fired up" this simply restarts it but hasn't caused any damage. At other times it has no effect unless of course the boiler has locked out in which case it gets reset for the next time it needs to start.

Comment by bernie at 20:57 on Tue 7 April 2009

Does anyone know where you can get a copy of the template letter to send to Potterton?

Comment by Colin Jack at 23:16 on Sun 21 June 2009


mines got a similar problem (had the pcb replaced already!)

mines fires up fine thou shuts down too early as it thinks its reached temperature, if i remove the temp sensor from the pipe it works fine (switches at .35 Mohms)

do you have a circuit diagram for the pcb?

Comment by andy at 15:45 on Fri 11 September 2009

Hi My Suprima 60 fires for two minutes then off for five, repeatedly,taking 2/3 hours before the rads reach temperature.I've had a thermister replaced which hasn't cured it.So I suspect the PCB Is the 'PCB' just a card or is it the whole unit that's fixed to the side of the boiler? As a retired electrician I shouldn't have any trouble replacing it, but any hints or tips would be a help. Also I've noticed from the 'comments' this problem hasn't come up before. Has anyone had it and cured it ?

Comment by Alan at 11:57 on Sun 11 October 2009

Hi Alan,

My memory of the suprima is a bit rusty, as I've moved house so have not had one apart in a while. I can't think of anything off the top of my head that would explain your problem. The PCB is a printed circuit board which is mounted vertically (if I remember correctly) on the right had side of the thing with the buttons etc on the edge. Removing some screws and a load of connects should allow you to extract it. Have a look at the soldering on the big connector pins. If the solder looks cracked, then that could be the problem - just resolder the joints. Otherwise try resoldering any joint that doesn't look perfect.


Comment by Gary at 21:45 on Mon 12 October 2009

My Potterton boiler is making loud noises. is there a danger of the boiler exploding or emitting CO2?

What would be causing this and could it be resolved by a maintenace check?


Comment by Tim Cronin at 10:46 on Tue 3 November 2009

i have potteryon legend back boiler and fire and from day one it has cut out and when firing up it makes a scary noise like a jet engine taking off and terrifies me and even neighbours hear it. husband has had many bits replaced at great cost over the years by reputable company but is still happend do often all our visitors know how we need to sit watching for red light cut out. i recon everyone shoulf get together and sue potterton for inconvienience.

Comment by wilma at 13:39 on Thu 12 November 2009

Suprimas are a joke and Potterton deserve to vanish without a trace. I have two of them and we're currently on circuit board no. 9 - we're now having to replace the new solid state improved boards which are - according to the local merchant - not as unreliable as the originals (how could they be?) but still unreliable. What is worst of all is the price they charge for the circuit boards - I mean you can buy a mini hifi with cd player, cassette and radio of less than £30.00 these days and sure it won't be very good but from my experience it will last longer than a Potterton PCB, most things will, cheese sandwich, pint of milk, just about anything you care to mention.....

Comment by LBuchan at 16:49 on Mon 18 January 2010

BBC have removed the Potterton letter template - here's a copy kindly posted by Despod on his blog -

Comment by Trax at 20:03 on Wed 24 February 2010

I have a Suprima 50 at home and a Suprima 30 in my Tenants house. Over ten years I have replaced PCBs twice in the 50 myself with again last year by British Gas. The new boards come inclusive of the whole control system and do seem more reliable. I have now just installed a new control system (£178) in my Tenants 30 due to lockout problems so hopefully that will now be more reliable. During this replacement I noticed a very loose and faulty (end melted) Thermister (£12) which can also cause lockout problems - worth checking, its just below the thermostat and much cheaper and easier as a first fix!

Comment by Rob Crawford at 21:38 on Mon 17 May 2010

Also, another problem with these boilers is the fire chanber fouling up.

I changed my PCB but it failed to cure the lockout problem. I was told to hoover out the fire chamber so I did and it cured the problem. It's easy to do and doesnt involve the gas side of the boiler.

Remove the right hand cover of the boiler, then the left hand cover. Remove the firebox frontplate (undo the big screw at the top and slide the plate down). In the firebox you will see lots of white debris. Use a brush and a vacume cleaner to remove the debris, especialy around the spark igniter. This may cure your problems.

For those interested in the techy bits, once the gas is lit the igniter sends a signal to the PCB called "flame detect" If the PCB does not recieve the "flame detect" signal it will lockout the boiler. Debris around the igniter and the firebox can block the "flame detect" signal.


Comment by david edwards at 7:59 on Wed 8 September 2010


Comment by BERNIE at 23:33 on Sat 1 January 2011

You are all risking your s and others lives by playing around with things you are not competent to test correctly afterwards, it is illegal to touch gas appliances unless you have been trained to do so for a reason, you could kill someone. Dont penny pinch, get it done by a gas engineer.

Comment by Colin Gardner at 8:32 on Fri 4 March 2011

As a qualified CORGI engineer and with a degree in Electronic and electrical engineering I must ask Mr. Gardener's to reconsider his comment.

Comment by BERNIE at 23:49 on Thu 31 March 2011

I have just had a potterton Suprima 50 EXPLODE at a rental property.. blown out window, shrapnel imbedded in wall... really luck that premisis was empty and heating was on constant low just to stop pipes freezing in cold snap whilst redecoration going on before new tenant goes in... that'll be delayed now. got pictures.. everyone who's seen it cannot understand whats happened.. am going to have to get a IGEM member to do a report for insurance.. nightmare.

Comment by Teresa at 10:07 on Wed 8 February 2012

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