Cold Radiator!!

[w3cvw]

Hi, one of my downstairs rads is cold, iv'e put on a new TRV and drained the system down, plus balanced the system, but it remains cold. Ive noticed that if i turn off the locksheild at the other end and open up the bolt to let the water drain out of the Rad then it starts to fill with hot water straight away??? Blocked pipe?? Any ideas would be appreciated.

 

[dcawkwell]

If you turn off all the other radiators and this one still doesn't get hot there is a blockage.

Turning off all the other radiators "might" free it.

 

[w3cvw]

If i turn off all the others then the cold one does get hot??? But as soon as i put the others back on it stops working again?? Not sure if its related but the pump gets VERY hot to the touch??