Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector X3 from the PCB

Measurement:

Test 1:
Measure the resistance between the Blue (3) and Brown (4) wires at the disconnected connector.
Expect approximately 170 Ohms.
Test 2:
Measure the resistance between the Brown wire (4) at the disconnected connector and Earth.
Expected resistance 1 MOhm or greater.
Test 3:
Measure the resistance between the Blue wire (3) at the disconnected connector and Earth
Expected resistance 1 MOhm or greater.