Potterton Suprima 30 with Boilermate II - What fun!

Hi all

If anyone has anything ideas about this i'd be grateful, before I spend out more money... thanks.

For almost 8 months I've had a intermittant problem with my central heating (potterton suprima 30 and boilermate II) as almost everyday the potterton has gone into lockout (red flashing light) and must be reset. After two plumbers replaced the overheat stat, ignition lead and electrode, pump and de-gunged the system I finally diagnosed the themostat on the boilermate as faulty, thus constantly requesting heat. The potterton has been firing every five minutes or so and switching itself off when it hits the temperature regulated by its own thermostat. The potterton eventually locks out and then there is no hot water for a shower the next day etc.

Having stood next to it when it shut down recently I measured the temperature of the flow pipe (the pipe taking the hot water back to the tank) to be about 70Celsius - so the lockout is not an overheating problem (the potterton will overheat at 90 i understand).

I pressed reset a few seconds after the boiler when off and it locked out again. I repeated this about 5 times and noticed that the potterton locks out at the moment when the green light is flashing rapidly (ie ignition). Looking through the window shows that the sparks are there but the ignition fails. the fan blows, the sparks spark but the gas does not light every time.

waiting 20 minutes or more the reset button fired up the boiler again and everything went back to normal.

I've this week replaced the thermostat on the boilermate and so this lockout problem is much less frequent now. To be clear, most of the time the potterton seems to work fine.Since the boilermate is not constantly requesting heat the boiler fires much less frequently and so this ignition problem occurs less frequently too (once in three days). However there is still a problem and I would like to sort it out. The plumber has suggested that it could be a sticky gas valve, or the PCB on the potterton or a sticky governor (external to the house I understand).

Can anyone think of any other causes and any way to sucessfully diagnose which of the possibilities it is?

thanks in advance

Andy

The usual problem with the Suprima is a duff PCB. Loads of info here and on Ebay!

Yeah definatly the PCB

When you change the PCB, you'll also need to change internal wiring in the boiler and the PCB housing. This is NOT a DIY job, IMHO. At the same time, it's worthwhile to fit new temperature and overheat sensors.

Note that there is not much value in fitting a new boiler onto an old Boilermate. To operate properly, the heatstore needs to be at 80 degrees or so, way above condensing temperature in a high-efficiency boiler, so it won't work at high efficiency! With new electronics, the Suprima will probably go on for several more years.

Fitting another old-style PCB is only a temporary fix!

Thanks everyone for your answers.

I see that the PCB is going to be everyones suggestion. After a little searching it's clear that the PCB's come up again and again. Originally my second plumber suggested it would be the PCB until he realised that the Boilermate was responsible for controlling the pump between the tank and the boiler. This might be a silly question, but what does the PCB in the boiler control if the boilermate does the pump? I.e. I had the impression that the PCB wasn't really doing anything because the Boilermate was controlling the system.

croydoncorgi, what do you mean about changing the internal wiring in the boiler and PCB housing?

Lastly, again, is there anyway to check it's the PCB not the gas valve? Please bear with me on this because I'm keen not to spend any mpre money before being sure that I'm targetting the right place.

Thanks once again

Andy

I have not encountered a sticking gas valve on your model.

Once I encountered a similar problem. It required the ignition electrode to be moved slightly along the burner bar to reliably light every time.

Before doing this I removed and seriously cleaned the burner first but that did not cure it.

Obviously anything like that should be done by a competent person.

Tony

SullyTheGoldfish said:

Thanks everyone for your answers.

croydoncorgi, what do you mean about changing the internal wiring in the boiler and PCB housing?

Lastly, again, is there anyway to check it's the PCB not the gas valve? Please bear with me on this because I'm keen not to spend any mpre money before being sure that I'm targetting the right place.

Thanks once again

Andy

Click to expand...

This is classic PCB failure on the Suprima. Virtually no doubt. The only way I can think of to prove the fault isn't intermittent gas valve failure is to fit a new one - but I've never seen a gas valve fail on a Suprima.

The new board comes fitted into a new control housing with all the internal wiring loom factory-attached. You completely dismantle the boiler and re-assemble it with the new board, housing and wiring.

Not a DIY thing really. Get a CORGI bloke in who knows his boilers.

Cheers,
Mike4

Hi All

Thanks for your replies - yet more poeple telling me it's the PCB!

Here's an idea: if it's the PCB then there should be cracked joints in the solder, right? So presumably an inspection of the PCB should tell me the answer quite quickly. Doh! why didn't I think of this before?!

Question: I'm competent to switch off the boiler, unscrew screws, and look closely with a magnifying glass but am not an electrician or a CORGI bod. Is there anything in the job of carefully inspecting the PCB that woud damage the boiler (ha, ha, can you break something that doesn't work??) or be dangerous? If anyone has instructions on this this procedure please could you post them or a link?

Thanks everyone, I'm almost cheered up about this!

Andy

Well, I shouldn't get overcome with emotion just yet.

Some Potterton PCBs have dry joints but the Suprima's problems are more deep seated. Consequently the design of the electronics has been changed 3 times, the last time with a Siemens board which is quite different to what went before.

Only a few Suprima PCBs fail because of a dry board joint, maybe you will be one of the lucky ones.....

Hmmm, I tried it. Maybe not such a brilliant idea - told me exactly nothing.

Back to uncheered.

FWIW I just had a problem with a Suprima 60 which looked like it was going to be the PCB although the Potterton fault finding chart was pointing to the air pressure switch. I tested the switch which seemed OK and with a bit of suck on the pipe to the pressure switch the boiler fired up reliably. It turned out to be a blocked air pipe fitting on the fan housing which was indicating to the electronics that the fan was not running. I suspect that the "horizontal" rear mounted flue has been installed through a 200 year old 2 foot stone wall with an upward slope to the outside which is allowing water (rain and maybe condensation) to run into the fan and collect near the pipe fitting. It was clogged completely with a white corrosion. Once cleared with a needle it is now performing perfectly again.