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
Disconnect plug X1C from PCB (3 way plug 3rd from left)

Measurement:

Test 1:
Measure the resistance between the blue and brown wires at X1C.
Expected resistance greater than 1MOhm (or O.L).
Test 2:
Measure for resistance between the brown wire at X1C to a suitable earth point.
Expected resistance greater than 1MOhm (or O.L).