Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove connector X7B from the PCB
Measurement:
Measure the resistance between each of the wires at connector X7B and the terminals at incoming terminal strip for the outdoor sensor.
Expect continuity / zero resistance and each of the wires in the harness.
Is the resistance measured as expected?
Expect continuity / zero resistance and each of the wires in the harness.
Is the resistance measured as expected?
Isolate as per TOPs P4
and refit as necessary