Potterton Puma 80 Pilot light always goes out - already changed the thermocouple

[riverthames]

The permananet pilot light on my Puma 80 lights ok when holding in the gas valve and sparking the piezo but it goes out when slowly releasing even after a few minutes. Water pressure is above 1 bar.

Changed the thermocouple but the effects are the same.

The diagnostic flowchart says 'suspect overheat thermostat'. Where do I find this?

I see from other postings on this forum that there may be a manual reset on some overheat stats/boiler models but it is not clear if this exists on the Puma 80?

Is this the correct line of attack or should I be looking elsewhere?

Thanks for your help - my wife is longing for a shower as the major gardening activities have also just started!

riverthames

[John Stumbles]

Is the pilot flame actually enveloping the thermocouple when it's alight?

[Ed Sirett]

This boiler is a fanned flue unit with permanent pilot light, a number of manufacturers had this designs (SD, Vokera, Pott. Puma...). It is essential to check the fan still operates at low revs when the boiler is idle. It is possible to get fans which stick (but are otherwise fine at full power) eventually the oxygen gets consumed in the combustion chamber and the pilot goes out. I used to think there ought to be enough incidental draughts to keep the pilot going but that is not the case.

[riverthames]

Many thanks for your responses - I tried out the following sequence and managed to clear the fault:

1) tested continuity on the overheat stat and that seemed fine 2) although the pilot light was visibly lit through the window it was not possible to confirm that the pilot light enveloped the thermocouple. Removed the front of the combustion chamber and cleaned it all out. 3) the pilot flight was actually very small - cleaning out the chamber must have freed some kind of blockage because next time the flame was much larger and played directly onto the thermocouple! 4) success! 5) only issue now is that the replacement thermocouple is only a push fit at the pilot light end and does not clip/screw into place - currently held up with a bulldog clip! 6) This has worked ok for a couple of days and so may be ok - I still have the original thermocouple and so may well put that back again if the new one pops out. All is well and a hot shower is most welcome after heavy landscaping in the garden!

Thanks again to all!