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 front facia from display PCB, refit PCB to boiler frame

Measurement:

Test 1. Measure for continuity (short circuit) between pin 1 (X6 ignition PCB)
and pin 1 (X4 display PCB).
Test 2. Measure for continuity (short circuit) between pin 2 (X6 ignition PCB)
and pin 2 (X4 display PCB).
Test 3. Measure for continuity (short circuit) between pin 4 (X6 ignition PCB)
and pin 4 (X4 display PCB).
Test 4. Measure for continuity (short circuit) between pin 5 (X6 ignition PCB)
and pin 5 (X4 display PCB).
Note.
Due to the small size of the connectors used on this appliance, harness checks are carried out from PCB connections.