CH / CHL means child lock.
This is to prevent small children from changing the temperature or touching the buttons on the heater. It can be activated and deactivated in the Mill app or directly on the heater.
Activate/deactivate child lock CH/CHL on Convection heater Generation 3:
Turn off the heater using the main switch on the right side.
Turn the heater back on using the main switch. Then, within 5 seconds, press and hold the gear button until you see CH/CHL in the display.
Release the button when CH/CHL appears.
Child lock is now activated/deactivated.
Activate/deactivate child lock in the app (for Generation 3):
Select the heater you want to activate/deactivate child lock on.
Scroll down to Child Lock. Here you can turn child lock on or off.
If the switch is green, child lock is activated.
If the switch is grey, child lock is deactivated.