Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect connectors X1 and X3 from the main PCB
Measurement:
Test 1:
Measure between the two wires of X1.
Resistance should be at least 1M Ohm.
Test 2:
Measure between pin 3 (blue) and pin 4 (brown) of X3.
Resistance should be at least 1M Ohm.
Measure between the two wires of X1.
Resistance should be at least 1M Ohm.
Test 2:
Measure between pin 3 (blue) and pin 4 (brown) of X3.
Resistance should be at least 1M Ohm.
Isolate as per TOPs P4
and refit as necessary