Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector switch in OFF position
CH temperature selector to MIN
DHW temperature selector to MAX
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:

Turn selector switch to the water heating position.
Allow burner to fire and water to heat.
Does the burner pressure modulate as the water temperature is satisfied?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.