Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Disconnect brown wire from terminal marked C on the air pressure switch
Measurement:
Measure resistance across the exposed spade terminal marked C and the terminal marked NC (white wire) on the air pressure switch.
Reconnect lead after test.
Reconnect lead after test.
Isolate as per TOPs P4
and refit as necessary