Set Appliance State:

CH Demand
Isolate Mains Power to appliance as per TOPs P4
Mode Switch in LOW position
Connect a U-gauge to the Burner Outlet Gas Pressure Point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the boiler to run its ignition sequence and the Pilot to ignite.
Power should be supplied to the Gas Valve and the U-gauge should indicate a positive gas pressure.
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.