Dnt knw where to find any info on this situation and just want to check if anything bad is going wrong with my heating circuit ---- one rad was cold at the top today and i bled it, and it took about 1 minute before water came out. it is ok now, but why only one radiator? second query is, some water that came out of the vent was a dark blackish colour, then it went clear. is this normal and i just worrying about nothing? is blackish colour normal? there are no signs of rust and nothing else is wrong (touch wood).