Set Appliance State:

Gas Off
Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Unplug both M3 & M5 from PCB

Measurement:

Turn on HW Tap.
Measure short circuit resistance between connector M3 connection 9 (Red) and connector M5 connection 19 (Orange) at disconnected plug.
Turn off HW Tap.
Measure open circuit resistance between connector M3 connection 9 (Red) and connector M5 connection 19 (Orange) at disconnected plug.
Replace plugs after test.