Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Operating switch in Water position
Temperature control to Max
Connect U gauge to burner pressure test point
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does main burner ignite at maximum gas pressure?
Note:
When U-gauge is removed pressure test point should be tightened & checked for gas soundness.