Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Thermostat turned to maximum
Connect a U-gauge to the Burner Gas Pressure Test Point
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to begin ignition sequence.
Monitor the burner pressure.
Does the burner pressure start at approximately 4mb then slowly ramp up over 6 seconds until it reaches operating pressure of 13.6mb?
Note:
When gauge is removed pressure test point should be tightened and checked for gas tightness.