Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the Thermostat 'On/Off function' multiplug
(two Orange/Black wires) from the PCB
Turn thermostat to Max position

Measurement:

1. Turn thermostat to Off position.
Measure the resistance across the two Orange/Black wires on the disconnected multiplug.
Expected resistance open circuit.
2. Turn thermostat to Max position.
Measure the resistance across the two Orange/Black wires on the disconnected multiplug.
Expected resistance close circuit.
Reconnect plug after the test.