Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Gain access to PCB (use Insulation Mat as required)
Disconnect connector X14 from the PCB

Measurement:

Test 1:
Measure the resistance between the brown and blue wires on the disconnected plug.
Resistance should be at least 1M Ohm.
Test 2:
Measure the resistance between the brown and the earth wire on the disconnected plug.
Resistance should be at least 1M Ohm.
Test 3:
Measure the resistance between the blue and the earth wire on the disconnected plug.
Resistance should be at least 1M Ohm.