RESISTANCE AIR PRESSURE SWITCH AT REST

Isolate Mains Power to appliance as per TOPs P4

Set Multimeter to Resistance

Remove the wires from the air pressure switch noting their locations

Measure the resistance between common and normally open terminals on the APS (terminals 1 and 3)
Expect open circuit.
Is the resistance as expected?

Note:
APS is shown removed for clarity but test is carried out with APS in situ with the air pressure tube connected.