18-12-2016, 10:47 PM
There won't be a resistance reading - they should all be completely open-circuit.
But when the flame is alight, a tiny DC ionisation current will be measured via the flame detection electrode. By "tiny", we're talking down at the uA level.
https://en.wikipedia.org/wiki/Flame_dete..._detection
https://en.wikipedia.org/wiki/Flame_rectification
If there is any other form of resistive leakage, that will affect the sensing electronics, locking out the boiler. The usual cause is debris from the heat exchanger. The condensate is acidic, and eats away at the heat exchanger, allowing grey particles in the combustion chamber. My last boiler - a first generation condensing boiler that was essentially a slightly modified standard unit - had the flame detection electrode at the bottom of the combustion chamber, and it took nearly exactly 12 months for the pile of damp crud to build up to the level required to make contact with the electrode and cause a lockout, which at least told us it was time to service it! Your boiler has the flame sense electrode at the top, so gravity should help to keep the stuff away from the electrode.
It could just be worn out, as you suggest. Or, it could be something else entirely. Good luck either way
But when the flame is alight, a tiny DC ionisation current will be measured via the flame detection electrode. By "tiny", we're talking down at the uA level.
https://en.wikipedia.org/wiki/Flame_dete..._detection
https://en.wikipedia.org/wiki/Flame_rectification
If there is any other form of resistive leakage, that will affect the sensing electronics, locking out the boiler. The usual cause is debris from the heat exchanger. The condensate is acidic, and eats away at the heat exchanger, allowing grey particles in the combustion chamber. My last boiler - a first generation condensing boiler that was essentially a slightly modified standard unit - had the flame detection electrode at the bottom of the combustion chamber, and it took nearly exactly 12 months for the pile of damp crud to build up to the level required to make contact with the electrode and cause a lockout, which at least told us it was time to service it! Your boiler has the flame sense electrode at the top, so gravity should help to keep the stuff away from the electrode.
It could just be worn out, as you suggest. Or, it could be something else entirely. Good luck either way
