My heat went out 2 years ago. Warranty Company authorized repair. Audi Dealer determined my Heater Core was bad. Replaced. Now part was back ordered, so I got it back after it had wamred up. So heat blew out of vents...winter came back around, and it was only producing heat at higher RPM's but only for a bit. Warranty Co was not good to work with on this so I let it pass and did not fight to have it repaired.

Since my heater core is new. What else could it be?

2001 Audi A4 Quattro, 2.8 liter

I have heard

1) Thermostat (which I may have replaced when they replace my timing belt & water pump.)

2) blower (although I have cold air- tested at 34 degrees)

3) A fuse

4) Some type of door in the air flow system

Can anyone suggest anything to me?