Set Appliance State:
Gas Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
Turn Hot Water Tap On
Boiler ON/OFF Switch OFF
CH Temperature Selector OFF
DHW Temperature Selector to Max
Disconnect green wires from Air Pressure Switch, and make safe
Attach Multimeter leads to terminals COM and NO (via crocodile clips) on the Air Pressure Switch
CH Temperature Selector OFF
DHW Temperature Selector to Max
Disconnect green wires from Air Pressure Switch, and make safe
Attach Multimeter leads to terminals COM and NO (via crocodile clips) on the Air Pressure Switch
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Observe multimeter, reading should be open circuit.
Boiler ON/OFF Switch ON.
Fan should start and Air Pressure Switch should operate.
Multimeter reading should be short circuit (zero resistance).
Mains power OFF.
Reconnect wires after test.
Boiler ON/OFF Switch ON.
Fan should start and Air Pressure Switch should operate.
Multimeter reading should be short circuit (zero resistance).
Mains power OFF.
Reconnect wires after test.
Isolate as per TOPs P4
and refit as necessary