Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Selector switch set to CH/DHW position
Boiler DHW thermostat set to MAX
Attach pressure gauge to burner pressure test point
Ensure appliance is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the burner to ignite and run on DHW.
With a flow rate of 10.2 litres/min, burner pressure will increase to approximately 9.4 mbar.
Reduce flow rate to approximately 4 litres/min via a DHW tap.
Does the burner pressure reduce?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.