i had the same problem tried flushing it out, but then it started leaking so ended up replacing heater matrix, quite a fiddle but not to bad to do took me 8 hrs, you will find you have to take the whole dashboard out top (easy) lower part of dash (not to bad) and then just when you think you are there you find on right hand drive cars you have take of the pedels and steering colume (easy) but anoying i got my matrix of ebay but get new orings oh by the way changing matrix is easy when you get to it!
steve gee
March 2006