damaged Bleed valve

i've just moved into a house which has a twin radiator in the kitchen, the problem is that the previous owner has sheared off the bleed valve in the rear unit?
how can i get the damaged piece out of the unit or is a new radiator the only answer

If it is just the vent insert that has sheared - the small square headed bit in a recess - then you should be able to undo the whole vent plug ~ 3/4" ish hexagon and put a new one in with a bit of ptfe tape. Alternatively, if there is a blanked boss at the other end of your radiator you could put a new vent in there.

...Unless of course the vent is directly into a welded-in boss, then you need to consider replacement if you can't get the little blighter out.

or the self tapping screw and o ring method

Years ago I visited a friend who lived in a bedsit - I couldn't work out why there were three connections to a radiator: bottom opposite ends and one of the top connections. This had a barrel ni-pple graunched in with an MF elbow and 1/2" steel pipe going up through the ceiling. Being curious/nosey, I got into the roof void and found that the F&E tank had 4 of these pipes used as additional open vents! Now that's a serious airlocking problem with a serious solution.