Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
DHW Demand
Thermostat turned to MAX
Connect a U-gauge to the Burner Gas Pressure Test Point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Run tap on maximum flow rate.
Allow the boiler to execute its ignition sequence and the burner to ignite.
Does the burner operate at 11.8 mbar of gas pressure?
Note:
When gauge is removed pressure test point should be tightened and checked for gas tightness.