Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW Demand
DHW thermostat turned to MAX
Undo Burner Gas Pressure test point
Connect a U-gauge to the Burner Gas Pressure Test Point
Put a Telegan temperature clamp on to DHW draw off pipe just above the thermistor
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to execute its ignition sequence and the burner to ignite.
Does the burner operate at approx 11.8 mbar and stay there until temperature reaches approx 50°C on the DHW draw off?
Note: Burner pressure should be adjusted if required.
Click on link for Gas Valve adjustment settings.
When gauge is removed pressure test point should be tightened and checked for gas tightness.