Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
Isolate Mains Power to appliance as per TOPs P4
Remove connector X4 from the PCB
Remove connector from CH sensor

Measurement:

Measure the resistance of each of the wires running to the CH sensor connector from X4 (pins 12 and 13)
Expect continuity / zero resistance on each test.
Also visually inspect the condition of the harness and its connectors.