Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
CH Demand
CH temperature control to max
Attach pressure gauge to gas valve outlet pressure test point
ON/OFF switch ON
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Gas must be OFF for this test.
Allow ignition sequence to commence fan running.
The pressure gauge should show a negative pressure of approx -4.5mbar.
Notes:
1.Lockout may occur after 5 attempts to ignite. If lockout occurs or the boiler is already in lockout then the reset will have to be depressed.
2.When "U" gauge is removed test point should be tightened and checked for gas tightness