Set Appliance State:

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

Observation:

Turn DHW temperature selector to MINIMUM to disable preheat, then turn back up to approximately 60°C (3 o'clock position).
Turn hot water tap ON.
Does the boiler react to a hot water demand?
(i.e. fan runs / burner ignites)