Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach pressure gauge to gas valve test point
Boiler Switch in ON position
Central Heating switch in OFF (central) position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow burner to ignite, is the burner pressure 14.3mb?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.