unable to bleed radiator with bleed key

[rezi]

hi, can anyone help?
my bedroom radiator is not heating at the top. The bottom heats one third up, the rest is cold. The bleed key will not turn the bleed valve, seems to have been rounded off.
my question is, is there any special tool to remove the bleed nipple from the valve in order to put a new one in and then use a bleed key? And where can you get it from?

 

[45yearsagasman]

View media item 35720 If it looks like this then they are available as a spare from plumbers merchants. Turn the rad off both sides and away you go.