Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
DHW temperature control to maximum
CH temperature control to minimum
ON/OFF switch in ON position
Attach U-gauge to gas valve outlet pressure test point
Set flow rate at tap to approximately 5 l/min
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow the fan to run and the ignition sequence to begin.
Once sparking is seen at the electrode there should be
approximately 1.5mb gas pressure shown on the U-gauge.
Does the gas pressure react as above?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.