Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Remove connector X15 from the PCB
Remove 1 wire from the overheat thermostat

Measurement:

Measure the resistance of both wires to the overheat thermostat from the PCB connector (X15) to the wires at the overheat thermostat.
Expect continuity / zero resistance on each of the wires.
Also visually inspect the condition of the harness.
Are the resistances measured as expected and is the harness in good condition?