Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect connector X3 from the PCB
Measurement:
Test 1:
Measure the resistance between pin 3 (blue) and pin 4 (brown) of the disconnected X3 plug.
Resistance should be approximately 160 Ohms.
Test 2:
Measure the resistance between pin 4 (brown) to a suitable earth point.
Resistance should be greater than 1M Ohm.
Measure the resistance between pin 3 (blue) and pin 4 (brown) of the disconnected X3 plug.
Resistance should be approximately 160 Ohms.
Test 2:
Measure the resistance between pin 4 (brown) to a suitable earth point.
Resistance should be greater than 1M Ohm.
Isolate as per TOPs P4
and refit as necessary