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:

Allow the boiler to execute its ignition sequence and the burner to ignite.
With the tap on full the burner should operate at 13.4 mbar.
Then turn down flow to approx 8 l/min and turn down HW stat to Midway.
Afterwards does burner start to modulate down as the temp increases out of the tap?
Or does it stay at 13.4 mbar?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.