Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach U-gauge to gas valve outlet pressure test point
Selector switch to DHW and CH position
CH temperature selector to Max
DHW temperature selector to Min
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow fan to run and ignition sequence to commence.
Does the burner ignite with a burner pressure approximately 2.3 mb?
Note:
When U-gauge is removed pressure test point should be tightened
and checked for gas soundness.