Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector 20 from the PCB

Measurement:

Test 1:
Measure the resistance between the brown and blue wires at
the disconnected connector.
Expected resistance greater than 180 ohms or greater.
Test 2:
Measure the resistance between the blue and a suitable earth connection.
Expected resistance greater than 1 Mohm
Test 3:
Measure the resistance between brown and a suitable earth connection.
Expected resistance greater than 1 Mohm