Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Attach a U-gauge to the outlet pressure test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to commence its ignition sequence.
Does U-gauge show a positive gas pressure?
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.