radiator hot at top and sides but not mid and bottom..please

hi there,
i just recent;y moved into a flat and when i moved in the heating was working perfect all the radiators were as hot as down under!but over the time off the last two weeks since i have properly moved in after doing it up they have all gone cold?well the main one near the boiler is hot around the edgers and top,but cold in the middle and bottom and some are just cold now or luke warm?can anyone advise me whats going on?i would just like to point out i have never bled a radiator and i have literally no clue to what i am doing,i saw my dad do it when i was young but thats about it!!sorry..please help if you can

cheers

sean

If the radiator is hot at both ends near the valve connections but cold in the middle at the bottom then you have sludge blocking the lower waterway. It indicates that the system needs flushing and cleaning. There is more info on this in the FAQ topic.