Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector M5 from the PCB

Measurement:

Test 1:
Measure the resistance between pins 28 and 29 on connector M5.
Expect a resistance of approximately 25 - 60 Ohms.
Test 2:
Measure the resistance between pin 28 and a suitable earth.
Expect a resistance of 1 Mohm or greater.
Are the resistances measured as expected?