Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Selector Switch ON
Gas Control Knob in Main Burner position
Remove the two Grey wires from the Air Pressure Switch and clip multimeter leads to the switch terminals
Selector Switch ON
Gas Control Knob in Main Burner position
Remove the two Grey wires from the Air Pressure Switch and clip multimeter leads to the switch terminals
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure short circuit resistance with the Fan running.
Replace wires.
Replace wires.
Isolate as per TOPs P4
and refit as necessary