Damsel in distress!

If it is a thermostatic rad valve you have, take the head off it and try and push the pin up and down as it could be stuck.

 

With the head off and the lock shield end fully open, put on a glove, clench your fist and with the side of your fist start to hit the radiator along the bottom. It could be there is sludge in the radiator and some vibration may just shift it.

 

When you released all the air - did a flow of water come out ?

 

Think it could still be the pin in the valve which although protruding is prob stuck down, if as you say it doesn't move. Get hold of the pin with a pair of pliers and try pulling it upwards.

 

Would it be worth turning off a few of the rads to increase the pressure to that radiator?

 

If the pin will not push down it is stuck, turn off all other rads, turn on heating and give the chrome valve body a few sharp taps with the handle of a large screwdriver, should clear it.

 

Did water come out the bleed valve when you let the air out? On my house when we had a combo fitted I had one rad off the wall and the plumber sorted the new boiler, when I fitted last rad I couldn't get it working and bled all air out but no water came out. Turned out I needed to fill the system up more to compensate for extra rad being fitted.

 

Jacqi2 says in post 3 that: Thanks Deleted member 11267, I've done that, no joy, the pin is up, although it doesn't push up and down, it came out altogether

 

The pins (push rods)
are not fixed to the valve that's why pulling on the pin does not work

 

As above put the pin back in and with luck all will be well, you are aiming to free the valve which has stuck to the seating, there is only a weak spring to lift it off so any **** (technical term) on the seating can stop it releasing full pressure from the system and a shock will usually free it, if not it's a new vale I'm afraid, I am assuming that the rad is full of water and that as asked in another post you get water out of the bleed point.

 

Had this issue last week myself. What i did was shut all the radiators off except the cold one. This forced the hot water into and through the cold one! Sounds like your system needs balancing.

Once rad is hot, turn the others on a little at a time.

Youtube have some vids on Balancing rads.