Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance

Measurement:

Disconnect the Yellow spaded wire (connection 3) and the White spaded wire (connection 6) from the Control Thermostat and measure the Resistance between connections 3 and 6 on the Thermostat.
With the Control Thermostat in the Off position, Resistance open circuit.
With the Control Thermostat in its high position, Resistance short circuit.