Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove one of the orange leads from the overheat thermostat

Measurement:

Measure resistance across the thermostat.
Expect continuity / zero resistance.
Note:
Overheat thermostat is located on the flow pipe towards the rear of the appliance.