House radiator problem?

I have a radiator upstairs in my house-not a combi boiler system-hot water tank system..1 radiator does not heat up..here what i know-- if i open the bleed valve at top right water comes out straight away..there is a drayton control valve at bottom left,i can pull the little pin out and no water leaks out,if i slacken either nut on the valve/conector that connects the pipe to the rad cold water leaks out from either..right hand side has a drain valve if i open it warm water comes out..So any ideas how to get this radiator warm or what the fault is..thanks