There are 2 hoses to the right of the battery that enter the vehicle, may or may not be covered by plastic
tubing

Remove cover and then remove the hoses

Flush with garden hose in & out both tubes.

If I recall correctly, there is no flow valve (open system).... heat is controlled via heater flaps in the
Heater Box Assembly... missing foam on the blend doors can cause "no heat" operation: (Google Search Image)

https://www.2carpros.com/images/external/IMG_03412.jpg

You could also have a broken Heater Control Lever that has popped out at the base of the Heater Box: (My youtube Video
off of an A5 VW Golf, but principal applies to your car as well).

http://www.youtube.com/watch?v=6U9ZdkAjdhQ&feature=plcp

The lever should not "drop" (9 to 11 second mark)... worst case, it will be lying on the floor not doing anything.

If your engine is running hot hot... overheating, then it is probably a bad water pump.

Thomas

Valve should be located on heater hose line near firewall. It probably has a cable that runs from the dash heat setting to the valve. It can get stuck or the valve can get stuck. Check the cable for free motion as well as the valve. To flush the system do the same as a radiator flush with the heat setting all the way hot. Also leave it at the hot setting when refilling to avoid air in the system.

Any luck finding the valve? I'd also be interested to know where it is....

If you follow the heater hoses from the engine to the firewall you will find it.