Some of the malfunctioning problems of the climate control can be reset by the dealer!!
I had mine reset recently after my climate control (C250D)switched from Celsius to Fahrenheit (and back) several times and stopped opening any ventilation ducts besides the windshield ones. I couldn't regulate the airflow at all and the only thing I had to do was resetting the system.
Otherwise it can be a bad temp.sensor inside the car which detects a lower temperature as is and therefore activates the full power of the heating system.
with a minor 600+k