Having moved house, we find one particular radiator doesn't heat up, despite the pipes that lead to it getting hot. One of the valves must be stuck, and I've worked out which one by feeling the pipes either side.
But how to unstick it? I've whacked the end with a hammer, and repeatedly twisted it round and round as far as it will go each way (it does rotate a little) but not had any luck.
Finally, I replaced all the valves. Looking at the old valve, it appeared to work fine, which puzzled me. Switching the boiler back on puzzled me even more - the radiator was as lukewarm as before!
Finally we realised all the hot water was flowing through the radiator immediately upstairs of the problem one - there must be some aspect of the pipework which means the water just can't be bothered to flow vertically downwards and back up for 7ft as well. If you turn the upstairs radiator valve right off, then the downstairs radiator will get almost as hot as the others. Almost.
Other downstairs radiators in the house have the same pipework coming down from the ceiling, and they get very hot. What could be different about the problem radiator?