Set Appliance State:

Mains Power Off
CH Demand
Ensure boiler is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Press reset lockout button on appliance.
Does the appliance now operate or does the fault code reappear?
If a different fault code is now displayed click here
Note:
It may take up to a minute before fault code reappears.