Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Remove the black and white wires from the air pressure switch
Measurement:
Measure the resistance between the two exposed terminals of the air pressure switch.
Expect continuity / zero resistance.
Is the resistance measured as expected?
Note:
The air pressure switch may differ in appearance but the colours of the wires remains the same.
Expect continuity / zero resistance.
Is the resistance measured as expected?
Note:
The air pressure switch may differ in appearance but the colours of the wires remains the same.
Isolate as per TOPs P4
and refit as necessary