Thermocouple

[Chris]

Ferroli Optima 701 boiler model. Got a problem with central heating...the boiler is failing to fire...or firing for a few seconds then dying (this is on constant 'heating' with the timer overridden). Water through hot taps is generally OK, though sometimes it misfires as well. The thermocouple looks a bit 'bright' through the viewing window. Does this seem likely to be the problem? Everything else seems fine, no noises or problems when the boiler's actually running. TIA

[Farmer Giles]

What do you mean 'the thermocouple is a bit bright'? I presume you mean the pilot light? The only way to check the thermocouple is to measure the small voltage produced by it when it is heated by the pilot. From memory this is about 30-40 millivolts.

[ARWadsworth]

But more likely to be the divertor valve.

Adam

[John G]

As this is a combi boiler is the system pressure high enough?

Also check that the pump is working when heating is on.

[Chris]

Yes, the end of the thermocouple fitting where the pilot light is. Instead of being black/grey, it's like when you blow out a match and it stays red for a few seconds, but it's like that all the time. Carbon?

[Chris]

Cheers.

[Chris]

Thanks, I'll fill it a bit more anyway.