Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Boiler Operating Switch in HW and CH position
Heating Control Thermostat adjusted to Maximum
Attach u-gauge to burner pressure test point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Does the burner ignite and go to its set working pressure?
Notes:
The CH output is range rated minimum burner pressure 2.4mb, maximum burner pressure 10mb.
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.