the heater matrix from new was always an issue, the tempreture and the combination of pressure caused as people know the matrix to go which as we all know is a pain in the rear end to change, a mod/recall was insigated and this is the heater bypass valve which allows water to circulate round the system bypassing the matrix, irstly if your car hasnt got one its very easy to tell, the inlet and outlet that go through the bulk head will be straight pipes and nothing attached, if the is one it will consist of a metal valve a plastic cylinder and it will be connected between the in and out for the heater matrix under the bonnet as shown by photos alreayd posted. as the valve gets old it stops allowing water to circulate through the heater matrix and only acts as a bypass hence the purpose. unless you are a real gambler i would replace as a matter of course when ever you by a car, its the equiv of changinf the cam bel to stop valve damage, they are about 30.00 last on i got from gsf, oem vw part as thats the only people who make them (some one may have started but for 30 quid get the quality one). hey take about 10 mins to change an if you have no leaks in your system and the engine is hitting normal temp this is hat it will be, i would strongly advise against running with out one, that said people have done for years and thee will be lots of golfs that have never had one. anyway a lot of waffle
basically, change the valve when you change yr car, rember check antifreeze mixture especially this time of year, hope hats of help Mo
