Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove ignition PCB from gas valve and remove cover,
leave connectors in place
Remove connector to DHW flow turbine

Measurement:

Test 1. Measure for continuity (short circuit) between pin 4 (X8 PCB)
and red lead DHW flow turbine connector.
Test 2. Measure for continuity (short circuit) between pin 11 (X8 PCB)
and white lead DHW flow turbine connector.
Test 3. Measure for continuity (short circuit) between pin 9 (X8 PCB)
and green lead DHW flow turbine connector.
Note.
Due to the small size of the connectors used on this appliance, harness checks are carried out from PCB connections.