Set Appliance State:

CH Demand
ECO mode ON
Ensure appliance is set to WINTER mode - NO sun symbol in display
(Press reset button briefly to toggle sun symbol on and off)
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 CH demand for 30 seconds.
Put the appliance into summer mode (press the reset button once a sun will appear in the display).
Observe the burner through the sight glass, as soon as the demand ends the burner should extinguish straight away.
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.