by htg engineer »
Wed Mar 24, 2010 10:56 am
Normally sludge/crap in system, quick fix remove radiators, flush outside with hosepipe and refit.
However it's an early sign of problems, you need to remove all radiators, flush system, add cleanser, flush system and add inhibitor - and hope you've caught it early enough - otherwise the boiler heat-ex may become choked.
htg