Set Appliance State:

Mains Power Off
Remove the selector control knob
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Turn the selector spindle to the OFF/Reset position (arrow pointing down)
Then refit the control knob and turn to CH/DHW position.
Has performing this operation deactivated the CO Function?
CO FUNCTION NOW DEACTIVATED
CO FUNCTION STILL ACTIVE