Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Boiler Operating Switch / Programmer set to WATER only
Connect a U-gauge to the burner pressure test point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

With the DHW tap fully open does the burner ignite and operate at maximum gas pressure of approximately 15.3mb?
Decrease the DHW flow from the tap to approximately 5 l/min.
Does the gas pressure modulate down as DHW temperature increases and is the DHW temperature maintained between 50-60 degrees C?
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.