CH / CHL means Child Lock. This function prevents small children from changing the temperature or pressing buttons on the heater. It can be enabled and disabled either in the Mill app or directly on the heater.
To toggle Child Lock on standard Gen3 heaters:
Turn the heater off using the main power switch.
Turn it back on, and within 5 seconds, press and hold the gear button.
After 3 seconds, the display will show CH or CHL – then release the button.
This will toggle the child lock on or off.
For Gen3M devices:
Press the gear button to enter the menu.
Use the + and – buttons to scroll until you see ChL on the display.
Press the gear button to activate Child Lock.
“ChL” will blink twice to confirm activation.
To disable Child Lock, quickly press the gear button 5 times in a row.
“NoL” will appear on the screen and the lock will be deactivated.
CO / COL means Commercial Lock.
This prevents anyone from changing the temperature or resetting the heater. It can only be activated via the app, but it can be manually deactivated on the heater.
To manually deactivate Commercial Lock (COL) on a Gen3M heater:
Press the gear button twice – the display will show 000.
Change the numbers to 123 using the + and – buttons.
Confirm each digit and the full sequence using the gear button.
“COL” will blink twice, and the lock will be removed.
If you make a mistake, press the Wi-Fi button to go back.