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Thread: Toto thermostatic shower valve fail

  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 . . .

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    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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    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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    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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    DIY Senior Member lifespeed's Avatar
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    It's happening again! Shower temp would fluctuate a little cooler than the 104 degree setpoint, then sometimes come back up. Manually increasing the setpoint did not increase the water temperature. However, turning it all the way cold, then back to midpoint (104) did result in the temperature going back to correct . . . for a while.

    I am really getting concerned about this. I have only had the valve for one month and this is the second apparent cartridge failure. What else could it be? The cartridge is responsible for the temperature. Last time I change it the problem disappeared, at least for a while.

    When I pulled the cartridge out I found no debris in the valve body. However, I did find some blue flecks on the brass body. I just assumed this was minor oxidation of the brass. The blue flecks were not loose, but appeared to be surface oxidation. I re-checked the hot water heater temperature, and it is at 125 degrees. I have now relocated the Noritz NRC-1111DVNG controller to the bathroom, so I can see the burner is still lit while this problem is occuring. I have no reason to believe there is an issue with the HWH.

    Anybody else use the TSTA valve? How does it work for you?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Both the thermostatically controlled valve and the tankless system have some hysteresis...it sounds like they're fighting each other. This whole thing is much easier with a tank verses a tankless...the temperature output of a tank varies much slower and more linearly than a tankless. You may have similar problems with any thermostatically controlled valve with any tankless. It depends on their speed of response to change and whether both can adequately respond to the other.
    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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    Quote Originally Posted by jadnashua View Post
    Both the thermostatically controlled valve and the tankless system have some hysteresis...
    No, that is not it.

    Apparently there is a third screen buried in this valve, associated with the 'service stops'. Thought I had checked them all, didn't know about this one. I'll pull it out and check it if I can locate a 23 mm socket.

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    checked the service stops, no screens are present. I did notice that the filter screens are an elaborate cartridge that are opened against spring pressure by water pressure. These could be suspect, although I could not see an obvious problem. They do work some of the time.

    Toto is sending yet another thermo cartridge, but this time they are sending replacement screens too. Hopefully that will do it. I blew out the valve both with water pressure and compressed air. Totally clean in there. And, in reality, a shower valve must operate in conditions that are less pristine than the new copper plumbing with filtered, softened water I have given it.

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    After replacing the screen/poppet assemblies and thermo cartridge number two the valve has been operating reliably for one week. The thermostat is only accurate to about +/- 1 degree, which is not bad, but the temperature difference can be felt slightly. At this point I am happy with it's performance. Toilet flushing or other water use has no effect.

    Personally, I suspect one of the screen/poppet assemblies was sticky, intermittently restricting the water flow.

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