Leaking radiator valve, can't pack

[Merlin83b]

After a recent drain of the central heating system, I've got two radiators that are leaking - they weren't before. Both valves of one and the lockshield of the other seem to be similarly constructed, though they're not from the same manufacturer.

I thought they'd just need repacking, but unscrewing gland nut (which I'm guessing isn't really a gland nut) also moves the embedded stem, and after a few turns the full pressure of the central heating sprays out of the gap between the valve body and the nut.

I've attached a picture showing where the water's dripping out - it's around the "stem".

Can this sort of valve be repaired? Will I have to drain the system to do it?

 

[oldbuffer]

1. Unless you know make and model of valve, virtually impossible to find parts. Even if you do know make and model, parts may not be available.
2. Replacing valves may well be the cheapest option.
3. Depending on what type of system you have (open vent, sealed, system, combi?) you might get away without draining down by changing one valve at a time.
4. Unless you have a pretty good grasp of plumbing, safer to drain down.