Hi there!
I had a problem with the Heater Matrix on my Vauxhall Cavalier 1995 and I was gonna remove it and replace it with a new one. I drained the coolant out and then pulled both pipes from the Heater Matrix. Even after unclipping them they were really hard to pull off!! You've probably just gotta keep pulling and twisting until they're free.
Anyway after I got my pipes off and half my dashboard out to remove the old Heater Matrix I realised that I didn't have enough clearance between the last bolt head and the floor of the car to remove it so I left it and went and asked some questions. It turned out that I didn't need to replace the old Heater Matrix. (The problem with it was it had a small hole in and my heating system was blowing steam out). All I done was go and buy a bottle of Radweld and added it to my coolant system, ran the car for a while and it sealed it!!
So if your problem's the same as mine was, go and get yourself some Radweld for about 3 Pounds, (actually the Barrs brand's better for Heater Matrices), pour it into the coolant tank, and cross your fingers!!
Otherwise flex your fingers and give them pipes a good pull!!
Good Luck!!
Glen
December 2005