One odd radiator

Hello

I have one oddly-behaving radiator in my bedroom. The rest of the radiators in the house, both upstairs and down, work fine but the one in the bedroom (a 'double one', just like all the others) seems to heat up then just cool down again - which isn't great when its trying to heat the biggest room in the house! The pipe leading to the radiator is hot (when the heatings on of course) but the rest of the radiator stays cool (sometimes the 'back' radiator is a little warmer but not overly so). I've tried bleeding it but no air comes out, only water. Any handy hints or suggestions are very gratefully received!

Has it got a thermostatic valve?

Check that both valves are open it sounds like the water is getting to the rad then stopping so a blockge of the return has occured (rad valve shut on return side)

try shutting down most of the other rads to see if it improves.

thanks all of you, it was the valves at the side! It appears that the plastic 'knob' (for want of a better word) had been swapped over before we moved in so we have been turning the radiator 'on' at the wrong end (the 'out' pipe) all the time!