Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach pressure gauge to fan pressure test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset appliance if required (press and hold reset button for 5 seconds then release).
Allow boiler to start it's ignition sequence (fan running).
Fan pressure should reach a negative pressure of approximately -2.5 mbar or greater.
(e.g. -3.0 mbar)
Notes:
1. The pressure measured will be negative.
2. When pressure gauge is removed, pressure test cap should be replaced.