I have 2002 A4 1.8T.
It got chilly in Michigan lately and when I turned on the heat, just the cold air came out of the vents (may be warm but not hot for sure). Took it to shop and they tried hosing out to see if there was any blockage..none. These are very nice guys at the shop, I had to mention.
Few observations:
- Coolant was hot going in but out was cold, mechanic said its most likely water pump not working/pushing coolant
- if pressed hard on gas, hot air starts blowing through the vents
- I had water pump changed early this year. Could it be water pump going bad again?

I searched this forum, but no one said anything about water pump when it comes to heating issue. Is there a way find it out? Codes?

Thanks