First step would be to check if the actuators work when you turn the knob.
Is the problem present in both sides when you run in two zone mode?
What about if you set it into mono mode?
Also check if warm water runs in to the heater system
If could also be the internal temperature sensor that indicates a too high internal tempearture but as there are two sensors in a two zone system the problem should then only be present in one side of the car.