Set Appliance State:

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

Observation:

Press the tap button until the preheat LED next to      is illuminated.
Does the boiler light for preheat demand then shut down once it has reached temperature?
Note:
Once test is complete turn preheat off by pressing the tap button until neither of the preheat LEDs are illuminated.