Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Attach U gauge to gas valve outlet test point
Remove 4 wire harness from fan
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the fan to run to full speed.
Measure the fan pressure.
Expect a negative pressure of approximately 6-8mb.
Note: When U-gauge is removed the pressure test point
should be tightened & checked for gas soundness.