Radiators in upstairs rooms cold in bottom half & hotter towards top, have tried normal routine of bleeding radiators but no air is expelled only water.

Cast iron? Radiators or baseboards? Separate loop or zone from the downstars system?

I don't know - some radiators are old the type with sort of dimples but they seem to be hot enough. It's the new ones that seem to be hot at the top. There are 6 new ones - probably been in about 3 years. One of these in the hall is hot all through. I think the new radiators are not on a loop but I don't know about the originals.
Thanks