Set Appliance State:

Gas Off
Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4

Measurement:

Resistance between connector M3 connection 15 (Black wire) and connection 14 (Brown wire) on the main PCB short circuit.
Resistance between connector M3 connection 15 (Black wire) and connection 13 (Blue wire) on the main PCB open circuit.