We "backflushed" my wife's heater core. A lot of sandy crap came out....A LOT. Afterwards, the heat came back! This certainly beat spending $2000 or so at the dealer for them to tear through the dashboard, put in a new heater core, but then end up with a lot of electrical issues since they didn't put the dashboard back together correctly...

 

Yep, that's why these forums are awesome. The dealer wouldn't have flushed it.

 

2000 a4 it has 1.8t and is around 120k on it, and it now has the heater stuck on all the time. i thought about pulling the fuse but i don't want to damage the system by doing so. any pointers is this a frequent problem?

thanks

 

Change the temp sensor mentioned above. It's cheap and easy and should be done preriodically since they fail a lot on these cars. Start the car cold and let it run to warm up. Keep a hand on the lower hose. As the engine warms, if the hoses warm at the same rate the thermostat is stuck open. It seems to happen more on the V6 cars but there's no reason why it couldn't be bad on yours. You have all the symptoms of a failed t-stat so I'd bet that's the issue. And I agree - remove the Mickey-mouse fan wiring setup and put in a new thermal switch to control the fan properly.