Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect plug ST15 from the PCB
Disconnect plug ST15 from the PCB
Measurement:
Test 1:
Measure the resistance between the blue and brown wires on the disconnected plug.
Resistance should be approximately 180 Ohms.
Test 2:
Measure the resistance between the brown wire on the disconnected plug to a suitable earth point.
Resistance should be greater than 1M Ohm.
Measure the resistance between the blue and brown wires on the disconnected plug.
Resistance should be approximately 180 Ohms.
Test 2:
Measure the resistance between the brown wire on the disconnected plug to a suitable earth point.
Resistance should be greater than 1M Ohm.
Isolate as per TOPs P4
and refit as necessary