Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect red leads from the overheat thermostat
CARE MUST BE TAKEN WHEN REMOVING THE WIRES FROM THE OVERHEAT STAT AS SURROUNDING COMPONENTS MAY BE EXTREMELY HOT

Measurement:

Measure resistance across the exposed terminals of the overheat thermostat.
Reconnect leads after test.
Note:
Ensure the appliance is still up to temperature.