Radiator not heating

[arsenal1]

2 story house, ofch about 18yrs old, about 18mths ago - The downstairs hall radiator (supplied and returns upstairs) was working ok until I put a nail through pipe (repaired by plummer) -- then after some re-adjusting of the heating balance got it working.
During the summer some modifictions to hallway with the radiator being raised abot 2", it hasnt heated since I have been bleeding on and off since I can only get heat into the radiator during bleeding but once stop it then cools down.
What I have noticed is that radiator now heats when bleeding from the otherside (I presume this may be due to the pressure head)

Can anyone suggest what I need to do to get heat to this radiator, all others are ok.

4 upstairs 3 downstairs

 

[wnjswozo]

turn off all rads and leave one on not working.this should force water throu.
then turn on the rest.if some get hotter quicker than others, turn these down lower

 

[arsenal1]

I have just tried this no suggest.
I have bled both vavles can get hot supply to both and into radiator but when left all goes cold even with all radiators off.
Any other suggestions?

 

[pauls]

have you checked the little brass pin inside the trv this may be stuck down if trv's have been locked off over summer

 

[wnjswozo]

was the water very dirty when you did alterations,if so could be sludged up,may have to cleanse system