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I managed to shear off the middle bit of my radiator bleed valve yesterday, just by turning it with a key.

The bleed valve went into a hex nut, which is ~11mm across.

I don't absolutely have to replace the bleed valve, because I have found I can still bleed the radiator by loosening the nut - it's just a bit more inconvenient than a radiator key.

I have found similar-looking things online called "Myson bleed valves" - but that comes with the warning that they only fit Myson radiators (I think because of imperial sizing), and I have no idea if this is a Myson - I don't think it is because the rad is doesn't match any of their sizes (it's 600x1200mm).

Is there a more generic name for these? Or is this going to be a Myson rad with this kind of valve?

  • I hope you get an answer, but I'd try a few other approaches: 1) Remove the whole valve and take it to a good plumbing supply store to match, 2) Buy every bleed valve I can find, because they cost about £2 and hope either one of them fits my radiator or one of their bleed screws fits my bleed valve. 3) Cut a small slit in the broken bleed screw shaft (with a small hacksaw) so I can turn it with a screwdriver.
    – jay613
    Commented Nov 2, 2021 at 9:22
  • All holes on the radiator should be threaded the same. If there is thread visible on the other connections then you could measure those as the baseline for the replacement nut. Commented Nov 2, 2021 at 11:36
  • @jay613 whenever I've tried slotting bleed valves for a screwdriver, they've been so stuck that a screwdriver just broke them some more. That's probably why it broke in the first place, as they're only brass. I'd be tempted to try a screw extractor and replace just the inner screw
    – Chris H
    Commented Nov 2, 2021 at 13:07

2 Answers 2


Is that rad upstairs or down? Can you isolate the rad easily or is the system built without individual isolating valves?
Do you really, really want to drain the entire system right now for a valve you can easily work around by using the outside nut, on a job you're unlikely to tackle again in the next half-decade?

If the answer to any of these questions is 'Bu@@er that for a game of soldiers!' then leave it til next time the system has to be drained anyway, for a bigger reason.
Then you can take out any working valve & schlep to the merchant's at leisure.

  • It's upstairs (in a loft room); boiler is on ground floor. The only isolation I have is the lockshield+TRV - which I was under the impression would be sufficient to isolate a single rad, but it still seemed quite flow-y when I closed the valves and loosened the nut a bit. It does feel very much like "nuts to this"; OTOH, I would rather fix it while I remember!
    – Andy
    Commented Nov 2, 2021 at 13:27
  • If someone had the sense to install a nice, accessible system drain you could drop the whole level to below that rad, then have at it. Otherwise, I'd wait… or consider how much faff is necessary without having to freeze the pipes to give you time to get to the merchant's & back before you run out of bowls ;). I'm all for doing jobs while they're fresh in mind, but always balanced with 'we can do it when we redecorate the front room next year'.
    – Tetsujin
    Commented Nov 2, 2021 at 13:33
  • doesn't look like there is a drain up here. The only one I know of is down on the ground floor.
    – Andy
    Commented Nov 2, 2021 at 13:35
  • If you open the bleed valve [or whole nut] & the valve[s] on that rad on the top floor, you can then drain it down from the ground floor until it's below the level of that rad. Takes a bit of guesswork, faff & periodic loosening of the bottom pipe/nut to test, but if you can't guarantee it will shut off & isolate properly, it's safest.
    – Tetsujin
    Commented Nov 2, 2021 at 13:38
  • I have 2 drains downstairs, none upstairs, but there is a just drain above the boiler (high on a downstairs wall) that I can run to a sink. The last little essential bit of a TRV can be unreasonably stiff if it's never been used.
    – Chris H
    Commented Nov 2, 2021 at 13:40

My approach

I'd be a little wary of relying on the outside nut long term in case of leaks developing. Most of my radiators need bleeding at this time of year, a couple of them more than once, so that might mean a few openings. New ones often have an o-ring seal which can tolerate opening, but older ones didn't.

The time to fix is either now or after this winter but before next winter. I'd go for the latter because I'd fit it in with work that's likely anyway then.

You should be able to isolate an individual radiator with its own valves, with the caveat that some thermostatic valves leak a little when turned off especially if the room gets cold (mainly old ones but not necessarily). The balancing valve on the other end, which is almost always present, can be reset by counting turns as you close it then opening it the same amount. You'll get some water out, and it will be dirty, so protect the floor, walls etc.

Personally, I know I need to drain, flush, descale, and refill, including inhibitor every couple of years anyway, because of a combination of hard water and the lowest point being a blower unit that easily clogs, in a room that needs the heat. Getting the sludge out of that is a good few hours' work; fixing this valve would be a minor addition to the effort. I'd one of each main type to have on hand, but consider it not guaranteed to fit so wouldn't remove the old one when the shops are shut.


I've done a little looking online. Most steel panel radiators seem to use 1/2" BSP, with Myson being a major exception (at least from the appearance). The one pictured in the question may well be smaller. Most valves you can buy have an O-ring seal under the nut (example). You might be able to see it if you look carefully, but possibly not. The older type is like this which also sometimes comes in a form that can stick out (like these 1/4"-thread valves), and relies on PTFE tape to make a seal.

Note that 1/2" doesn't refer to any physical dimension of the part, but of the pipe that thread was originally used with.

  • I hadn't considered descaling. Not a job I've ever had to do on a heating system. Last 'wet' heating I had, I lived in an area where no-one ever descales a kettle, let alone heating.
    – Tetsujin
    Commented Nov 2, 2021 at 13:18
  • @Tetsujin I was originally going to comment on your answer instead. My part of Bristol's water comes form the Cotswolds and is rather harder than some of London's (I see you and the OP are both there, by your profiles) but we had plenty of limescale where I grew up in Greenwich. In fact SE18 and BS36 have very similar values. TBH though the scale is a smaller part of the problem than the sludge, at least since I got a condensing boiler a few years ago. You remind me that my kettle is due descaling!
    – Chris H
    Commented Nov 2, 2021 at 13:30
  • @ChrisH I'd love to say that everything is better in SE9... but no, the water is really hard here too.
    – Andy
    Commented Nov 2, 2021 at 13:33
  • I come from Leeds. Kettles really never need descaling. After maybe 5… or 10 years they get a bit of very very thin brownish residue, that's it. I now live in London where you can nail the water to the walls in sheets.
    – Tetsujin
    Commented Nov 2, 2021 at 13:35
  • @Andy I went to school in SE9. Can't comment on the water though, but I was almost certainly on the same water supply at home (top of Shooters Hill, near the defunct water tower)
    – Chris H
    Commented Nov 2, 2021 at 13:35

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