Set Appliance State:

Ensure boiler is cool
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 a fault code is displayed, reset boiler.
Does the boiler reset & show the boiler flow temperature?
Note:
If the boiler fault code changes from the original to a different fault code, then CLICK HERE.