Good afternoon and thanks for allowing me to join, my daughters car is a 64 plate A3 1.6tdi and the heater remains cold. 
The reservoir is full and temperature gauge upto mid range position but no heat coming out of the vents. I’ve tried finding the heater control valve on the gearbox end of the engine but it doesn’t appear to be there, any suggestions as to its location and if I need to be looking elsewhere for the problem?

 Thanks in advance.

Tony.

Before delving into the dashboard consider if this might be the cause of your problem:

https://www.youtube.com/watch?v=39ngHGvMzEg

 

Hello Clifford, I removed the expansion tank a couple of years ago and it didn’t have one of those in anyway but may have been removed by the previous owner because it was causing issues, possibly leading to a blocked matrix. I’ve currently got a piece of 22mm heater hose on the matrix exit port on the bulkhead with boiled  water in it but as yet there’s no flow through it.

Well if there is no flow through the matrix then it is blocked. Have you tried flushing with mains pressure water in the reverse direction? Some folk suggest a pressure washer but I have reservations about whether the system is capable of withstanding 100 bar pressure.

If you are searching for a water flow control valve, there isn't one. That system was dropped years ago in favour of flaps in the air ducts to regulate temperature.

Thanks Clifford that’s the information that I was looking for, control valve not there anymore, I was beginning to think that some nugget designer had placed it on the inside of the bulkhead. No there’s no flow through the matrix in the reverse direction so I’m now going to order a new matrix.

Once again thanks for that information 👍