Set Appliance State:

Turn Hot Water Tap On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the fan to run, burner to ignite and establish and the appliance to run with a DHW demand for 30 seconds.
Turn hot water tap OFF.
Observe the burner through the sight glass, as soon as the demand ends the burner should extinguish.
Does the burner remain alight or extinguish straight away?
Note:
This test is to confirm the gas valve is closing as soon as the demand ends.