Why don't my 2004 Z4 blow hot air?

Thank you very much Jim. I understand "clogged heater core or faulty temp door", but not sure what the climate control head is or where it's located. I am planning on trying to fix this myself, so any additional help would be great. Thanks again...

One last question, Jim. Are the parts you mention: heater core, temp door and climate control head, accessible without having to remove the dashboard? I really appreciate your help with this. Happy New Year..

DARN! This could be a major project for a DIY'er, it sounds like.

You seem quite knowledgeable on this stuff, so I have one more question, if I may. I have noticed a knocking sound from what appears to be the front of the engine. I am not talking about the common valve ticking in BMWs, but a louder noise that occurs primarily on cold starts and at low RPMs. Once the engine is warm it goes away. I realize it will be a challenge to diagnose, without actually listening to the engine, I was thinking perhaps a stretched timing chain clanking against the TB cover or something like that, but since they are made of metal, is that even a plausible explanation?

Thank you! You are good. Do you work on these cars on a daily basis and if so, do you live in the DFW area by any chance?