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Thread: Toto thermostatic shower valve fail

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  1. #1
    DIY Senior Member lifespeed's Avatar
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    Default Toto thermostatic shower valve fail

    Got a new Toto TSTAR thermostatic shower valve to go with my copper re-pipe. Sort of worked for a couple days, then I could no longer turn it up over 104F. When I run the shower in the adjacent sink the water comes out of the tankless HWH at 125F no problem. But when I do that the water actually cools coming out of the shower!!

    This makes no sense at all. I cleaned the screens in the shower valve, the brass body gets plenty hot from the hot water coming in, the stupid thermostat just doesn't let it out. I 'calibrated' according to Toto instructions, but all that does is set the maximum temp, which it is incapable of achieving. And what is this with the shower cooling when the hot faucet is turned on?? The shower is 1" to 3/4" pipe, and the faucet comes off the same 1" pipe to 1/2". No way I have a significant pressure drop in the pipe or a lack of hot water supply with the biggest Noritz HWH.

    That thermostat isn't working. $600+ valve and trim and this is what I get? Grrrr . . .

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    What kind of volume are you trying to get at the shower/tub? A tankless system will drop its outlet temp if you exceed its ability to produce hot water.

    Regardless of the size of the supply pipe, the internal restrictions on the tankless may mean that the (likely higher) volume available on the cold side is disrupting the pressure balance function inside the valve ( if it has one). Some thermostatic valves have both the temp control, and internal pressure balance safety functions. If the available volume is not the same on both the hot and cold sides, it can shut down. It may not be the valve's fault, but it may not be a good match to your supply.

    Make sure that you have the hot/cold lines hooked up properly to the valve (not swapped).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Senior Member lifespeed's Avatar
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    I appreciate the suggestions to check the obvious, but this has already been done. As posted previously, I can get 125 degree water out of the bathroom sink at the same time the shower valve fails to get hotter than 104 degrees. I have a Noritz NRC-1111DVNG, which has more than enough capacity to run two showers, let a lone a single 2.5 GPM shower and a faucet. I also chose this tankless because it has a large heat exchanger and less pressure drop than most other models.

    I have plenty of volume and pressure on both the hot and cold. The plumbing is brand new and 1" from underneath the shower wall all the way to the main in the street, and also to the hot water heater.

    Toto is sending a new thermostatic cartridge. They claim this is not a common problem. Weird.

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    Plumber jimbo's Avatar
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    It would be worth discussing with Noritz their recommendations regarding pressure balancing and/or thermostatic valves with the tankless. It is a combination which can be challenging.

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    DIY Senior Member lifespeed's Avatar
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    Quote Originally Posted by jimbo View Post
    It would be worth discussing with Noritz their recommendations regarding pressure balancing and/or thermostatic valves with the tankless. It is a combination which can be challenging.
    Really? Can you provide any detail or what in particular I should look for? Everything is already installed. If there is some fundamental flaw with tankless and thermostatic valves I'm not sure what I can do at this point.

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    DIY Senior Member lifespeed's Avatar
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    More than a week later, via the slow boat on UPS ground, the new thermostatic cartridge arrives from Toto customer repentance. All is well, I can flush toilets and turn faucets on and off with impunity - the water temperature is rock steady. The temperature knob actually changes the temperature now, going from 120 degrees all the way down to cold. The midpoint labeled at 104 degrees is a calibrated 104.

    It is a very nice and kid-friendly valve (there is a lockout that must be pushed to get up to 120 degrees). It is unfortunate they didn't ship me a working unit, but I suppose if manufacturers were held to a standard of perfection they would all fail.

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