I have a normal 4 bedroom house gas central heating, with one execption, that about 20 years ago i teed off
and added a large double rad in the lounge extension, and as far as i am aware it has worked fine

it is the furthest from the boiler/pumps etc, and is also the lowest point of the whole system

Problem now is, that rad is only hot at the top 1/3 , and cold at the bottom
ive tried bleeding it, and thats fine, just clean water and no air comes out

All the other rads in the house seem fine, and again minimul bleeding required

I suppose my next option is to remove the rad, and flush it through,, but its a BIG bugger and bloody heavy!

Any ideas ??

I think you'll find it's full of sludge and needs a flush out. I did 2 of mine some years ago by taking the rads off. There are flushing products but I don't think I'd be too keen on sending the sludge round the rest of the system to drain down several times. I've just extended the house and added several rads which involved a lot of draining down, filling flushing, draining and re-filling. It takes forever.
Have you got corrosion inhibitor in the system (Fernox or similar)?

Just get the rad off and drain it.

When you fill up stick a litre a Sentinel X400 in it for two weeks, fully flush and then some X100 inhibitor.

thanks guys, i presumed it was a sludge issue, and its placing in the house means that it would be a sump, for any crap

So next day off, its coming off the wall

And yes i have rust inhibotor in there

Steve