After working faultlessly for 23 years the following fault has developed:
Fan comes on
Sparks
Pilot light comes on
Main burner lights
Stops sparking
Burns as normal for 8 seconds or so
So far all as normal
After 8 seconds the main burner flames and the pilot light (as observed through the window) *slowly* die over about 3 seconds - they become progressivley thinner, lift off and waver, and then extinguish.
*Only then* click as the (main burner?) solenoid valve turns off
Go back to top - starts sparking again for about 13 seconds, with pilot attempting initially weakly to light and finally lighting strongly, and repeats indefinitely. There is no solenoid valve clicking while this is going on - I think the pilot gas supply is on all the time.
I deduce from the above that there is not enough throughput of air - but I have examined the flue/intake very carefully and it seems to be clear, and the boiler was cleaned only 6 months ago.
Does this diagnosis sound correct?
Could the fan be failing so that though apparently running normally it is only delivering a fraction of the intended pressure, which is neverthe less sufficient for the controller to think its working correctly?
Fan comes on
Sparks
Pilot light comes on
Main burner lights
Stops sparking
Burns as normal for 8 seconds or so
So far all as normal
After 8 seconds the main burner flames and the pilot light (as observed through the window) *slowly* die over about 3 seconds - they become progressivley thinner, lift off and waver, and then extinguish.
*Only then* click as the (main burner?) solenoid valve turns off
Go back to top - starts sparking again for about 13 seconds, with pilot attempting initially weakly to light and finally lighting strongly, and repeats indefinitely. There is no solenoid valve clicking while this is going on - I think the pilot gas supply is on all the time.
I deduce from the above that there is not enough throughput of air - but I have examined the flue/intake very carefully and it seems to be clear, and the boiler was cleaned only 6 months ago.
Does this diagnosis sound correct?
Could the fan be failing so that though apparently running normally it is only delivering a fraction of the intended pressure, which is neverthe less sufficient for the controller to think its working correctly?