Set Appliance State:

Mains Power Off
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 enter standby or does the fault code reappear?
Appliance Enters Standby
(Continue fault finding from start sequence)
Fault Code Reoccurs
If a different fault code is shown click HERE