Potterton Puma 100 - Pilot Light Goes Out / Won't Stay Lit

[mikexxx]

I have a Potterton Puma 100 Combi boiler which, apart from a pump replaced after 9 months, has been relatively trouble free in the 5 years it has been fitted. It is mounted on an outside wall in my garage.
However, over the last 2-3 months there has been a number of instances where the pilot light keeps going out. I noticed that the pilot light would go out after the hot water tap had been on. When you heard a glugging sound in the pipes and checked the pilot light you could guarantee it would have gone out. I've also noticed sometimes that the boiler stays on after the hot tap has been turned off but I can't say 100% whether this happens all the time.

Usually it can be re-lit and the boiler fires up and I have hot water and central heating again. Then about two weeks ago the pilot light wouldn't light at all and the gas valve was replaced. After that the pilot would light ok but would still keep going out when the hot water tap had been turned on. Then about a week ago the pilot light went out, it lit ok but when I released the knob the pilot light went straight out. I've tried holding the burner knob in for 2-3 minutes but the light still goes out and nothing I can do can keep the light on. When the engineer visits he gets the boiler going but a few hours after he leaves the pilot goes off and won't stay on when lit. So at the moment I have no hot water or heating (difficult when you have two young children as well) and the engineer is scheduled for another visit tomorrow which will be his 4th in the last 7 days.

The gas pressure has been checked and it is ok.

I have had the heating engineer at my house so many times over the past three months I've lost count and he is baffled as to why the pilot light goes off after the hot water has been on. He also can't seem to solve the problem of why the pilot won't stay on after it has been lit. I have been very lucky in that he doesn't charge call out fees and hasn't charged me for each visit but so far I must have spent around £400 on parts and labour which include the gas valve, thermo couple, full system drain and re-fill, full service, strip down and clean.

If I had a crystal ball at the start I may have been better off with a new boiler. But the boiler is only 5 years old and I feel I should get longer out of it than that. I did think of contacting Potterton and asking for an engineer visit but that will probably be costly.

Any help from any experts on here would be greatly appreciated. Sorry it's a bit long winded. I hope I have explained myself clearly enough but if you need to ask anything further please do so. Many thanks. Mike

 

[ChrisR]

Sounds to me (in a grumpy mood because of bloody computers, router, blue bloody yonder...) that you've beed comprehensively ripped off by an incompetent prat.

This has been covered many times on the forum, but it must be getting hard to find an old one by now, so here it is again...

Very standard puma fault, the DHW (tap) water flow switch sticks in the ON position. You can tell if you look at the pcb - a red light should come on only when the hw flows, and go off immediately it stops. If the switch sticks, the boiler carries on, heating the radiators.
It's looking at the tap water pipe which isn't getting any hot water through it so the boiler thinks it should try harder so it carries on.
And on, until it overheats, and puts the pilot out.
In the overheated condition you wouldn't expect to be able to relight the pilot. You'd have to wait until it's cooled.

New operating part about £40, new electrical part about £10, + a callout.

 

[mikexxx]

ChrisR, thanks for your comments, appreciate it.

Does what you say explain why the pilot light won't stay lit after releasing the Gas Control knob? I tried lighting it this morning after it had been off all night and tried again about an hour ago. The pilot light lit ok on both occasions but just won't stay on.