Set Appliance State:

Gas On; Pilot On
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Selector Switch OFF
Gas Control Knob in Main Burner position
Connect U-gauge to pressure test point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

With main burner alight, check burner pressure is greater than 2 mbar.
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.