[quote="htg engineer"]The Pilot electrode (FSD) senses the flame, this sends the signal down the HT lead to the PCB.
Check the flame is touching the electrode, if it is then it could be the pilot assembly, HT lead, or PCB at fault - hard to say without seeing the boiler.
Allure fire front ? or other ?
No doubt you are correct as moving the eht lead did indeed solve it thanks for that
I would however love to know the mechanism of how the flame is detected as the eht lead is just connected to earth via the secondary of a high step up transformer I sort of reason maybe the resistance of the spark gap increases suddenly with the temperature rise to stop the spark at that point causing the spark to jump the internal gap on the pcb instead and it is this change that is sensed to open the gas valve
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