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 connections to flow thermistor

Measurement:

Test 1. Measure for continuity (short circuit) between
pin 8 (X8 PCB) and red lead removed connector.
Test 2. Measure for continuity (short circuit) between
pin 16 (X8 PCB) and black lead removed connector.
Note.
Due to the small size of the connectors used on this appliance,
harness checks are carried out from PCB connections.