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 X5 from the PCB

Measurement:

Measure the resistance between the leftmost green wire at the disconnected plug on X5 marked 11.1 and a suitable earth point.
Resistance should be greater than 1M Ohm.