My plumber installed new shower diverter-spout below. The last one was dripping. While working, he also misaligned the shower top knob incorrectly, so Hot Side brings cold water, and Cold side brings hot water reversed.

We're bringing plumber back to fix next week. While I operate in this reversed mode, will it cause any damage to the diverter/spout I just installed? Or nothing to worry about? He didn't even replace the cartridge, was just rescrewing the top shower knob etc to fix the slight dripping/leak.

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  • 2
    I don’t see a problem and it will be great entertainment when your brother-in-law uses the shower.
    – Lee Sam
    Commented Jan 6, 2022 at 8:54
  • 1
    The "cold side" plastics won't melt if they get some hot water on them, so you're good to go for a week.
    – FreeMan
    Commented Jan 6, 2022 at 12:53
  • 1
    No, nothing will be damaged. Your knob will just work in reverse until it's fixed.
    – MonkeyZeus
    Commented Jan 6, 2022 at 13:14
  • take off the handle ... spin the valve stem 180 degrees ... reinstall handle ... should be ok now
    – jsotola
    Commented Jan 8, 2022 at 1:30

2 Answers 2


It's NOT just 2 valves on a joystick.

It may not work, and can scald you

Almost any valve of this type has a thermal protection feature. If the water temp becomes too high, it forcibly blends in water from the "cold" terminal.

And that is an important feature, as the Flint water crisis exposed the fact that legionella and other bacteria happily thrive in water heaters not kept hot enough. "Hot enough" is in the scalding range, making such valves essential to using a safe water heater.

(These facts are well known, but not yet "hardware store guy" common knowledge).

If your valve sees too-hot water, it will add water from the "cold" terminal, but on your valve this will make the water hotter and hotter still, creating a thermal runaway that WILL scald you.

Make the plumber fix it.

  • interesting, thanks, everyone else in comments said its no big deal, glad you mentioned, I had plumber fix it today
    – mattsmith5
    Commented Jan 7, 2022 at 23:34

That looks like a moen single-handle faucet cartridge unit. No problem running it reversed.

  • Reversal of hot and cold may be just a matter of removing the cartridge and replacing it in the correct orientation Commented Jan 6, 2022 at 22:49
  • @Phil that would be nice, but should be done or the hot would be uncontrollable in an over-temp situation. Commented Jan 7, 2022 at 23:25

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