Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove the wires from the fan overheat thermostat

Measurement:

Measure resistance between one terminal of the fan overheat thermostat and the one securing screw (it does not matter which terminal or which screw).
Expect open circuit (O.L).
Is the resistance measured as expected?