Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Boiler On/Off Switch ON
Connect a U-Gauge to the Gas Valve outlet pressure test point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Does the U-Gauge indicate a positive gas pressure?
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.