Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect the white lead from the air pressure switch
Measurement:
Measure the resistance between white wire
connection and blue wire.
Resistance should be closed circuit.
connection and blue wire.
Resistance should be closed circuit.
Isolate as per TOPs P4
and refit as necessary