[kstiglich]

Hi Guys,
I have an X3 E83 2007 and my heating air conditioning is not working. My cold a/c works perfectly but when try to set temp to warmer temperatures, I have no air coming from the vents. The blower works fine because it is the same for cold or warm air, and it works on cold air. I have been researching and have three alternatives, but want to confirm with you prior to buy any part.

First alternative is that the heating control valve (water) is failed and it does not let the warm water enter into the heater core. But I scanned my car and I do not have any fault code...do you know if there is a fault code for this?
The second alternative is that the heater core is clogged and do not let warm water come into it. Does it raise a fault code?
The third option is a AUC Heating sensor, that can be clogged, but I understand that it would work only when recirculation is active?
I have a fault code: 20 AUC heating sensor, but I am not sure if it is new or old code.

So my questions are....do you have any process to discard which one is the failed part? and why if any of these is failed I do not have ANY air coming from my vents when set my temperature very warm? Does the vents have a thermometer that read the temp and found it is not hot so it does not open a door or something similar that do not allow any air from the heater coming into the cabin through the vents?

Any help would be appreciated.