Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect the 4 pin plug from the fan and make safe
Attach U-gauge to POUT at the top left of the gas valve
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Fan will run at maximum speed.
Does the U-gauge show a fan pressure
of approximately 4.5mb or greater?
Note:
When U-gauge is removed ensure all disturbed
joints are checked for gas tightness.