Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to Resistance 
CH Demand
Disconnect leads from the Air Pressure Switch and make safe
Attach the multimeter Probes to the Air Pressure Switch Terminals
ON/OFF Switch in OFF Position
CH Temp Selector in Maximum position
DHW Temp Selector in Minimum position
Mode Selector Switch in Heat and Hot water position
Attach the multimeter Probes to the Air Pressure Switch Terminals
ON/OFF Switch in OFF Position
CH Temp Selector in Maximum position
DHW Temp Selector in Minimum position
Mode Selector Switch in Heat and Hot water position
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
If required reset boiler, turn CH / DHW control to reset position.
Multimeter should be reading open circuit.
While observing the multimeter, turn ON the boiler ON/OFF switch.
When the Fan runs and the Air Pressure Switch operates, the multimeter reading should change from open circuit to closed circuit.
Multimeter should be reading open circuit.
While observing the multimeter, turn ON the boiler ON/OFF switch.
When the Fan runs and the Air Pressure Switch operates, the multimeter reading should change from open circuit to closed circuit.
Isolate as per TOPs P4
and refit as necessary