Lack of air flow is a vent door issue which could explain the lack of heat.
The heater core might seem to be free from flushing (not clogged), but chances are that it is (will pass enough
coolant for flow testing, but not enough to transfer heat).
If all the vent doors are working correctly, remove the dash and replace heater core.
I had little heat on a Jetta yesterday. Flush seemed, but when I pulled the core I could see that it was plugged.
I can post a video link later tonight.
Manual or Climatronic heater panel? Checking heater / vent door function is more involved than I can explain here.
Wednesday, December 12th, 2012 AT 7:27 PM