Set Appliance State:

Mains Power Off
Reinstate power to appliance after 20 seconds has elapsed
Ensure No demands are present
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Cancel boiler purge / self-check (reset) if required.
If fault code is displayed, reset boiler.
Does the display show the CH temperature setting?
Note:
If the boiler fault code changes from the original to a different fault code, then CLICK HERE.