Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach pressure gauge to the inlet pressure test point
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset boiler if required.
Allow ignition sequence to commence.
Does the pressure gauge show an acceptable minimum
gas inlet pressure of at least 19mb (NG) or 35mb (LPG) throughout its operation ?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.