Most likely cause would be the pump sticking, if as you state the microswitches on the diverter valve are making, the pump can be ruled out. Other things to test:
20vdc to the solenoid, test between the solenoid and N9 on the motherboard (and an audible click when it is being activated), the voltage runs through the CH overheat stat, so if you haven't got 20v, check the stat is closed circuit.
PD Valve, on the front of the gas valve, there is a pressure differential valve (three screws removes it although it remains served by two copper tubes), start the boiler and feel the push rod, if it doesn't move, the PD valve and or tubes are blocked, when pushing forward (normal operation), this allows gas through the valve to the solenoid.
Carefree
November 2011
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