I had this issue with my heaters not working around 12 months ago. Thought it was caused by the silica bag in the expansion tank. I replaced the tank and cut the old one open. The bag was still intact so I replaced the matrix and the issue was resolved.


Recently decided to change my cambelt / water pump as it was well over due. 66 plate Passat with 85000 miles on clock. Removed water pump and found the metal part that electronically closes over the impeller was partially disintegrated! so it looks like the issue with the blocked matrix was likely caused by pieces of metal from the water pump!


I have flushed the system a few times now, so fingers crossed I wont suffer the same issue on the new heater matrix!

Water Pump.jpg