Set Appliance State:

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

Observation:

If required, reset boiler.
Allow self-check to complete and ignition sequence to commence.
Inlet pressure should remain above 17.4mb (N.G.) or 25mb (L.P.G.) throughout the ignition sequence.