Set Appliance State:

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

Observation:

Monitor the inlet pressure as boiler carries out its ignition sequence.
Does the inlet pressure remain satisfactory throughout the boiler ignition sequence?
Note:
When U-gauge is removed the pressure test point should be tightened and checked for gas tightness.
Refer to TOPs for further information on acceptable gas inlet pressures.