Right so this worked for one cycle. I turned all other rads off and the one which wasn't working got hot and it stayed like that for one cycle. I balanced all other rads and now it's not working again. It's almost like the water in that rad just isn't heating up.
I have a radiator in my living room which is not getting hot, water is coming through the valves and it's been bled. I drained it and changed one of the valves' (not TRVs) when I filled the rad back up the pipe on the right hand side got hot but now it's gone cold again (valve fully open) the...