Hi guys need some help as I am getting really annoyed with this boiler. Its around five years old I have had it powerflushed 2 times in the last year and half. The heating all work fine but the water side is problem. I have taken the secondary heat exchanger out 5-6 times in the last years as it keeps on clogging up with black iron or something. This is only on the water side and not the CH side, as when I take the secondary heat Exchanger out its just on that side!!! Can anyone advise? Some say I should get the boiler descaled? Also the boiler makes loud sound when you run the DHW. Few people have sugested I just change the Sec heat exchanger but my concern is if there is dirt there is no point as it will just clogg the heat exchanger again? By the way its a combi boiler. Also i was told these boilers have auto vent and so hence do not need bleeding? Please help?? Today I again drained the boiler as the boiler kept going out!! aargh. Cleaned the sec heat exchanger and when I took the pipe connection for the expansion vessel some black iron crap also came out. Maybe that explains why I am losing pressure everytime the heating is on. Due to blockage?