My heating system works fine, except for one upstairs rad which stays completely cold. The feed pipes to and from it are also cold. I have bled it and there is no air and the pin on the TRV moves freely. I've tried turning all the other rads off to send all of the hot water to the cold rad, but that hasn't made any difference.
I've recently moved into the house and I'd guess the heating system is 15 or so years old. The system comprises 2 rads downstairs and 3 rads plus a heated towel rail upstairs. Any ideas?
You could turn off the two valves and let some water out of the bleed valve to depressure the rad. When you close the bleed valve and re open the valves you could see if it repressurises, using the bleed valve again. The point is it would answer Steves question about whether or not the rad is connected - unless you have a mega blockage.
It would also be interesting to see if you cracked the nuts under the valves whether or not water would flow, but you would have to know what you are doing (turn the boiler off, expect a mess, put the system back to the correct pressure, remove any new airlocks, maybe add some more inhibitor etc)