Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect the six way connector from the top of the PCB housing

Measurement:

Measure resistance across the thermostat connections (2 endmost black wires, connections 5 & 6 as shown) at the disconnected connector.
Expected resistance closed circuit (zero ohms plus resistance of test leads).