Set Appliance State:

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

Measurement:

Test 1:
Measure the resistance between pins 9 and 18 on X20 connector.
Resistance should be approximately 42 Ohms.
Test 2:
Measure the resistance between pin 9 on X20
to a suitable earth point.
Resistance should be greater than 1M Ohm.