Set Appliance State:

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

Observation:

Allow 3 minute self check to complete.
As boiler reaches the end of the self check monitor the inlet pressure.
Does the inlet pressure remain above
18mbar (NG) or 37mbar (LPG) throughout?