These symbols mean that Child lock or Commercial lock is activated on the heater. When these locks are active, the heater cannot be controlled via the control panel. If you wish to disable the lock, do the following:
Turn off the heater using the main switch. Turn the heater back on, and within 5 seconds, press and hold the gear button. After 3 seconds, the display will show "CH" or "CHL," at which point you can release the button. The heater has now activated or deactivated the child lock.
For Generation 3M units, follow the steps below to activate/deactivate the "child lock" function:
Press the gear button to enter the menu. Use the + and - buttons to navigate the menu until you see "ChL" on the display. Press the gear button to activate the "Child lock." "ChL" will blink on the display twice, indicating that the child lock is activated. To unlock, quickly press the "insert settings icon" 5 times. "NoL" will appear on the screen, and the child lock will be deactivated.
CO/COL indicates the commercial lock. This prevents anyone from adjusting the temperature or resetting the heater in any way.