Set Appliance State:

Mains Power Off
Selector switch set to DHW/CH
Ensure boiler is Cool and NO demand for DHW and CH
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset boiler.
Does the boiler reset?
Note.
1. To reset boiler, turn selector knob to the reset position for 1 second.
Reset is confirmed by 0 displayed.
2. If the boiler fails to reset and a fault code other than L1 appears CLICK HERE.