Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Attach pressure gauge to burner pressure test point
DHW temperature selector to MAX position
CH temperature selector to 0 position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Reset lockout as necessary.
Allow fan to run.
Does the gauge show a pressure of at least 2mb?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.