How can I fix a thermostatic radiator valve?

I have an oil fired central heating system. All my radiators are very hot apart from the one in the living room which is ice cold. I have taken the radiator off, flushed it out with a hose, re-fitted, turned on the valves and bled it, but the radiator is still ice cold. After searching the internet I believe it may be a faulty thermostatic radiator valve. Any thoughts?