Set Appliance State:
Gas Off
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect green leads from the air pressure switch and make safe
Attach multimeter probe leads to the exposed terminals of the air pressure switch
Ensure there is a demand to heat the thermal store - this can be achieved by running the DHW with power turned off to the appliance
Observe multimeter reading, resistance should be open circuit.
Disconnect green leads from the air pressure switch and make safe
Attach multimeter probe leads to the exposed terminals of the air pressure switch
Ensure there is a demand to heat the thermal store - this can be achieved by running the DHW with power turned off to the appliance
Observe multimeter reading, resistance should be open circuit.
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Allow combustion fan to run while observing multimeter.
Does the resistance reading change to short circuit?
Mains Power Off.
Replace leads after test.
Does the resistance reading change to short circuit?
Mains Power Off.
Replace leads after test.
Isolate as per TOPs P4
and refit as necessary