Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
ECO mode On (no preheat)
Reset the appliance if in lockout
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Ensure the appliance has been reset from lockout
Does the burner ignite and establish for at least 10 seconds?
Note:
The flame can be seen via the viewing window at the top of the heat exchanger.