Worn bleed valve - do I need to replace radiator??

[OOPS]

I have newish radiators, removed for redocration have replaced and now need to bleed to get the central heating back on. It is the first time I have had to bleed it and the thread has gone, the key spins no grip. I read the note that they are a pig to get out, but I don't know where to begin getting it out. It is also a roll top single radiator with he bleed valve at the back top left and is hard to get at in situ Is there an easy solution?

 

[ChrisR]

You could try reshaping the end of the key. They're often countersunk so they're longest at the outside. Make it so its longest at the inside, if you see what I mean.

You could cut a slot for a screwdriver if you have a Dremel type tool (mini drill) and a cutting disc about 15mm diameter.
Otherwise it's rad off, drill with left hand drill and use a screw extractor.

 

[MANDATE]

Are you absolutely sure the thread has gone? I think it would need a fair amount of force to strip the thread, Not only that you would have a continous leak. It is more likely the square section of the valve has become rounded or the square hole hole in the key has opened up.
It could be the key was too large, so I would obtain another key and ensure it is a good fit. I have found that keys do vary a bit in size.
If it's the valve, you might try a small ring spanner, I would think around 6 or 7 or 8mm, fit the spanner and push the end towards the wall slightly to take up any looseness before turning it. Make sure you turn it anticlockwise.