Cold areas on my radiators

[darrenmichael]

My wife and I have just moved into a new flat. We put the central heating on for the first time and although it works pretty well, we've noticed that the lower areas of the radiators are cold whilst the top parts are hot and functioning normally.I understand that bleeding the radiator works if the problem is the other way around but how can I fix this?

 

[Bahco]

Could be sludge in the system which will mean removal and flushing of rads

 

[Rincewind]

i guess being in a flat you have a combi boiler? If so draining and flushing system is best. When it drained down add sentinel X400 via a radiator top, and refill and bleed. When you refill dont chugg in to much water (1 to 1.5 bar). Leave it in for a week or two then drain and flush out well. Stick in a dose of sentinel X100 and re-fill