Morning everyone, I've drained and refilled my sealed CH system a few times and have a problem with a rad at the top of the house. It is cold, while all other rads are piping hot. The thing is, it doesn't seem to have a problem with flow. As the system refills, I bleed it and the air comes up and out as the rad fills back up. So there's flow at least. I guess it's possible for the return not to be working but the other rads on the same floor don't seem to have an issue. I opened up the floorboards and found they've taken a spur direct to the rad valves from somewhere (and these pipes are also cold when heating is on). The other thing is, I presumed there would be no problem after fixing other issues on the system (damaged exp vessel and surrounding pipework), so I used this same rad to pour in a chemical cleaner (Flomasta CH Cleaner). I left it in the system for 2 days and went to drain it this morning and the water was clear - I think it is possible it never made its way around the system because of this dodgy rad. Should I follow the pipework back to where a hot pipe meets a cold pipe and see if there could be a blockage? Or maybe there is bad plumbing where both rad feeds are coming off one pipe or something equally silly. Any ideas? I checked the pump also, it is working fine.