Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove connector X15 from PCB and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to complete its self-check.
If fault code is displayed, reset boiler.
Does the display show the boiler flow temperature?
Note.
PCB connector numbers can be found on the board.