I took my Audi A6 to Drysk Autos Ltd because I was having problems with the heater blowing cold air ( occaionally luke warm ) they diagnosed the fault to be a blocked heater matrix. Opinions from other garages had be vague and ranging from head gasket to air lock. Drysk Autos were on the button. They gave me a quote for the repair which I accepted and now the heater is superb.