The mixing valve.

My shower is a hedonistic wonder.

When we remodeled the bathroom, one of the things we did was have two shower heads—with separate temperature controls—installed. One of these also has a diverter that can send water to the shower head, the tub filler, or a hand shower. It’s great.

But one day about 10 years ago, the diverter (which in day-to-day use is hardly ever moved from “shower”), stopped working quite right. If you did shift it, sometimes it would send water where you wanted, sometimes it would split water between two of the settings, sometimes just half the expected water would come out and not always where you wanted, etc. Something was clearly amiss. But it wasn’t leaking, so I fiddled with it until it was sending all the water to the shower and stopped touching it, because I couldn’t afford to have it repaired.

Until someone (a houseguest, I think) moved it, and it went all wonky again. I got fed up.

I did a little Internet research, and learned that I really just needed to pull the handle off, unscrew the core, and replace it. So I tried to do that. Got the knob off no problem. Got a valve tool and tried to get the core out. But the people who installed it had done so before the tiles were put on. And the tile guy cut the hole big enough to clear the stem…but not big enough to clear the core.

So I went around to the other side of the wall: my bedroom.

When we remodeled the bathroom, we also had a sink installed in the bedroom. I highly recommend this. It’s awesome. Especially if you only have one bathroom; being able to shave and brush teeth and deal with contacts and all that without blocking the bathroom really helps. The relevant point about that for this story is that there is a medicine cabinet installed in the wall in the bedroom above the bedroom sink. Which is conveniently right where the diverter is on the other side. So I unmounted the cabinet, and had complete access to the entire valve complex.

The right thing to do seemed to be to cut the valve out of the plumbing, repair it, and use pipe repair sleeves to solder it back into place. So I got a hacksaw and cut the pipes. But the valve was still trapped by the framing, because it had been installed from the other side, before the wall was put up. So I got out my Roto-Zip and cut the valve out of the framing. Some of the pipes leading to/from it are not very long, but I left as much length as possible to have space for the repair sleeves.

When I set the Roto-Zip down after cutting the framing, I saw the tile cutting bit in the case. Let me say right now that 2 minutes after you’ve done the wrong thing is not a good time to realize what the right thing to do is. I should have used the Roto-Zip to enlarge the hole in the tile to clear the core. That would have been the right thing to do. But it was too late now. And the course I was on was straightforward enough.

I replaced the core; it took about 15 minutes. When I pulled the old core out I saw that what had happened was that that rubber sleeve seal with the complex holes that does the mixing and diverting had worn such that it was no longer secured to the core. So whenever the handle was moved the rubber sleeve would shift via friction and change what was going where, but there was no correlation anymore between the holes in the brass and the intended holes in the rubber, so it was all random what would go where. (While the valve was out I also used the Roto-Zip to enlarge the hole in the tile.)

Once the new core was in the valve it was a simple matter to set the valve back in place, slide the repair sleeves over the cuts, and solder everything back in place.


It turns out that the valve is a big chunk of brass. A really big, really thermally-conductive chunk of brass.  Getting enough heat onto the pipes and sleeves to get it soldered together turned out to be impossible without setting the house on fire. Setting the house on fire is good to avoid. So no problem: they make plumbers’ epoxy for a reason, right?


Epoxy will stick to almost anything. It’s great, amazing, wonderful stuff. It’ll stick to pretty much anything except copper.

There followed about 8 months of trying various formulations of epoxy, trying to find something that would stick to the copper pipes well enough to hold back water pressure. I finally did find one. I don’t recall what it was. It doesn’t matter: The takeaway here is not “Use this wonder epoxy!” it’s “Don’t try to glue copper because it won’t work and you will weep.”

Through all of this of course, the shower was still perfectly functional, because the shower has two shower heads with separate controls. So while all hell was breaking loose on the north end of the shower, the south end was working just fine (except for the day-and-a-half in the middle where the hot water on that side would not shut all the way off. But that was a couple of hours to pull the core and replace it. There, the hole in the tile was big enough).

(Of all the major systems in my house, the plumbing is the one you will probably read about most. Because it is truly cursed. Someday soon I’ll write up the story of the Sh*tgyzer, a completely different adventure which happened to take place one day during the 8 months the diverter project was happening.)


A guy in his early 50s, living more or less alone in a 90-year-old house, trying to keep it all together.

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Posted in Plumbing
3 comments on “The mixing valve.
  1. chriso says:

    I remember this…

  2. aedifica says:

    I think you’ve just answered my puzzlement about the hot water handle in my bathroom, which keeps changing its mind about what position is “off.” (It’s a lever handle and theoretically all the way back is off, but in practice off is often somewhere in the middle and pushing it the rest of the way back starts the water flowing again.) It sounds like it might be the same thing going on as you described here:

    So whenever the handle was moved the rubber sleeve would shift via friction and change what was going where, but there was no correlation anymore between the holes in the brass and the intended holes in the rubber, so it was all random what would go where.


    • Erik says:

      It sounds like a similar problem, yes. Although usually a simple on/off valve is not made this way (with the rubber sleeve seal).

      Usually a valve for a single-temperature tap either has a rubber disk that presses against a brass orifice to seal it (the older type; generally speaking if turning the knob harder to “off” stops or slows a drip, this is what you have), or a pair of very smooth ceramic disks that have matching orifices such that one disk rotates against the other to match/close off the holes (the newer type; generally speaking if your handle only turns 90 or 180 degrees from “off” to “on”, this is what you have).

      From your description of the problem it sounds like you have a ceramic disk type and the moving disk has broken free of its connection with the stem. So moving the stem shifts it by friction, but it’s not really OK anymore (like my rubber sleeve).

      Barring strange things like my “hole in the tile too small” issue, replacing the ceramic cartridge is very easy. A screwdriver, a wrench (if the valve is in the wall you may need to buy a “valve wrench set”, which is a set of pressed-steel tubular things of different sizes that are long enough to reach into the wall and get around the core to turn it), and a trip to a big-box home improvement store or plumbing supply for the new core and you should be able to fix it in under an hour.

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