Set Appliance State:

Gas Off
Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove plugs M3 and M5 from the PCB

Measurement:

Check for short circuit resistance across connector M3 connection 10 (Red) and connector M5 connection 26 (Red) at disconnected plugs.
Replace plugs M3 and M5 after test.