hi its the iron oxide from the rads ie corrosion. that flows into the heat exchanger this blocks and causes the water flow shortage u can keep cleaning it best way is a powerflush flush cleaning fluid in hot water with the heat ex dipped in it this dissolve the waste. and best to fit a filter ie magntec to the return boiler pipe which collects debri and can be washed out add inhibitor to the system this will prevent any further corrosion. the heat ex works by passing c h water through one side out the other and cold flowing through the one and hot out the other there are fine fins inside which allow the ch water to pass along the cold without touching each other causing the cold water to become warm causing hot water thats why its named heat ex as it exchanges heat
kash, September 2010
