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.
Status code 231 is usually caused by the power to the appliance being interrupted whilst it is in a fault code.
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 enters standby - retest appliance
Boiler will not reset or resets and returns to status code 231
Different fault code shown