Pilot light issues - Potterton Puma 80 combi

[rsmid]

Hi All

I'm having a few problems with the pilot light remaining on..... It has been going off intermittently but re-starting OK. I've had a CORGI out and he thought it was the AAV. "It is full of scale and has been leaking - may not be opening and may be triggering the pilot light"

The whole unit is about 8 years old and has been serviced each year (last time May 2005).

Today the pilot light has gone off and won't re-light. I've opened up the combustion chamber and it now re-lights and stays on.

Trouble is, as soon as I put the combustion chamber lid back on, it locks-out within about 20 seconds and won't re-light until I open up the chamber again. I've sat with it running for 20 mins now - chamber open and no problems.

It doesn't seem to make any difference whether it is HW or CH running.
Any idea's?

 

[corgigazza]

1:may have blocked pilot injector or the thermocouple may have slipped down slightly, should be clamped by nut onto stem of thermocouple
2:The fan should run also at low speed constant then go fast when the burner lights.
3:Check the flue outlet is not obsructed.

 

[rsmid]

Thanks Corgigazza

1) Checked the pilot injector - good flame running over the thermocouple. Will try removing and re-tightening the thermocouple.
2) Fan does exactly that
3) Flue vents straight up above the roof (boiler is in the loft), so I'll have check that in the daylight tomorrow.

Is there any chance that the Thermocouple is getting too much heat when the chamber is all closed and therefore cutting the pilot light or is that not possible?

 

[ChrisR]

The wind from the fan can pull the pilot about such that the thermocouple cools when the cover is on. Try a new thermocouple, they do age. It's a special tc, a "Universal" is almost ok but not quite - they slip.
This is of course highly dangerous specialised work which takes years of experience for a full appreciation if the risks, so expect a bolt of lightning from CORGI.

 

[rsmid]

Cheers ChrisR - I'll report back once it's been replaced. It does look like the original, so it may well be past it's best.

 

[rsmid]

I re-seated the TC and got a new one just in case.
At the same time, I gave the hot water flow switch a little squirt of WD40 in case it was sticking. And guess what - so far no problems!
Might be a co-incidence as the TC might have slipped down a little.
Anyway, I'm a happy chappy for now
Thanks for the advice