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:

Measure the resistance across the two orange/black wires on the disconnected multiplug.
Expect continuity / zero resistance.
Is the resistance measured as expected?

Reconnect plug after test.