Set Appliance State:

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

Measurement:

Remove and inspect the harness (limit thermostat and air pressure switch) for signs of damage and continuity.
The harness runs from connector PL1 on the PCB to the limit thermostat and the air pressure switch.
Replace harness after test.