In the the living room, all other rads working well. Inlet pipe is red hot, very small amount of heat in top of radiator but rest cold. Outlet pipe is not cold but not warm, if that makes sense. I did have other cold radiators but these were fixed, clean out of sludge and re balance. Since then only one hasn't worked, he things the system needs a full flush as there maybe a blockage to last radiator - but why would in pipe be so hot ?. I have just bled all radiators and some black dirty water came out first in most of them and then ran clear. My question is, should I go for a system flush or is it the last radiator needs replacing ?