Set Appliance State:

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

Measurement:

With the Main Burner alight is the Gas Valve outlet pressure within the range of 13.45 - 12.75mbar?
Note: When U-gauge is removed pressure test point should be tightened & checked for gas soundness.