Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap ON
DHW Temperature Control to MAX
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).
Fan pressure will read negative and should be approximately -1.5 mbar or greater.
(e.g. -2.0 mbar)
Notes:
1. The pressure measured will be negative.
2. When pressure gauge is removed, pressure test cap must be replaced.