Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
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 (press and hold reset button for 5 seconds then release).
Operate boiler at maximum output. CLICK HERE FOR INSTRUCTIONS
Fan pressure will read negative and be greater than -3.9mb
Notes:
1. The pressure measured will be negative.
2. When pressure gauge is removed, pressure test cap should be replaced.