Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector X20 from the PCB

Measurement:

Test 1:
Measure the resistance between pins 1 & 9 on connector X20.
Expected resistance approximately 44.0 Ohms.
Test 2:
Measure the resistance between pin 1 on connector X20
and an earth connection (use the copper pipe to the gas valve as earth).
Expect a reading of approximately 1 MOhm or greater.
Are the resistances measured as expected?