Set Appliance State:

Gas On; Pilot On
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector switch in HW position
Attach U-gauge to burner pressure test point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

When Burner ignites does burner pressure increases to maximum with a DHW flow rate greater than 9 litres per minute?
Note:
When U-gauge is removed pressure point should be tightened & checked for gas soundness.