Set Appliance State:

Gas Off
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Connect U gauge to inlet pressure test point
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Measure the pressure as the boiler commences its ignition sequence
Expect 18.5mb continuously throughout the process
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.