Set Appliance State:

Ensure NO demands are present
Ensure boiler is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the appliance to complete its self-check.
If fault code F2 is displayed, reset the appliance.
Does the display show the appliance flow temperature?
Note.
If after appliance reset the fault code changes from the original to a different fault code, then CLICK HERE