I'd actually forgotten that until Tony dug up the old post. Yes the pcb didn't match the cct diagram. Caps drying up often make the board fail as the overlap times get short. Board also fails if (as sounds the case in your boiler) the resistance of the relay contacts is above a fraction of an ohm. Thermocouples work with of the order of 10mA and 10mV, so with one ohm you lose all your voltage across the relay contact instead of the solenoid.
