Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector X2 from the PCB

Measurement:

Test 1:
Measure the resistance between pins 3 and 4 on connector X2.
Expect a resistance of 1 MOhm or greater.
Test 2:
Test the resistance between the Brown (3) of the disconnected X2 connector and a suitable Earth
Expect a resistance of 1 MOhm or greater.