Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
ECO mode ON (no preheat)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does the fan run, burner ignite and establish?
Note:
The flame can be seen via the viewing mirror at the top of the appliance. (some versions of this boiler do not have this facility)