Set Appliance State:

Mains Power Off
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset the boiler as necessary.
Does the appliance now complete its self check and go to standby mode (status 203), or does it return to fault code?
Boiler resets and goes to standby - retest appliance.
Boiler will not reset or resets and returns to fault code.
Note:
If appliance has reset from this fault code previously and then ran but the fault has reoccurred select "Boiler will not reset or resets and returns to fault code".