Audi Repair: Heater Stays On, vacuum leak, heater valve

Question
1997 Audi A6 Quatro - My heater won't turn off regardless of the temp setting.  Is there a way to manually bi-pass the controller and close the valve for the heater hose?  Is the valve a normally open or normally closed valve?  I thought that would tell me if the problem was the controller or the valve.
Thanks for your help!

Answer
Hi,  the heater valve is normally operated by vacuum, it is located where the two hot water pipes go through the firewall.  Look for the valve, and get someone to change the temp setting with the engine running to see if it is still moving.  If not, suspect a vacuum leak, you can check operation of the valve by manually moving it but be careful, a lot of plastic is used in the contruction, and these plastic parts are expensive!  Let me know,  Jan