Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Connect a U-gauge to the burner pressure test point
Selector Switch in DHW position
Gas On
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 continue to operate at maximum gas pressure of 11.1mb +/- 0.5mb?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.