Set Appliance State:
Gas Off
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
Turn Hot Water Tap On
Selector switch to Off position
CH temperature selector to Min
DHW temperature selector to Max
CH temperature selector to Min
DHW temperature selector to Max
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Selector switch to DHW position.
Allow fan to run.
Check for voltage between the black wire on the air pressure switch and a suitable neutral
Mains voltage should be present.
Allow fan to run.
Check for voltage between the black wire on the air pressure switch and a suitable neutral
Mains voltage should be present.
Isolate as per TOPs P4
and refit as necessary