The heat is not blowing out of the vents.
If the fan control knob is not functioning, it's likely the blower fan is not being turned on. Replace the knob panel (they tend to wear out anyways) and see if that helps. If not, then the blower fan died (or it's associated fuse). Best of luck.
Search Volkswagen Passat Questions
Volkswagen Passat Experts
Related Models For Sale
Used Cars For Sale