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Thread: Grohe Thermostatic valve install Question

  1. #1

    Default Grohe Thermostatic valve install Question

    OK -- I'm a bit confused about the Grotherm Thermostatic valve and how I am supposed to install it with the volume controls. There are two inlets -- one hot and one cold, and two outlets, one to the shower and one to the tub. This is going in a tub & shower application.... I thought that one volume control / shut off would go in-line to each fixture (one to the shower and one to the tub) from each outlet. But, when I talked to the plumbing supply house to confirm, they told me that I should cap the bottom outlet, T off the line coming out of the top, install the valves off the T, send one line up to the shower and one down to the tub. This seems a bit odd to me as it requires some creative in wall plumbing to get everything to line up. Other showers I have done were not nearly this complicated. Is this correct? Any advice?

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Depends...are you going to use a divertor in the tub filler spout, or a separate valve? If you are going to use a diverter valve, then one volume control would be fine. Actually, cap one end and run it to the volume control, then either t off to both the tub filler (with divertor) and the shower head, or to a separate divertor. There should be some instructions in the box...what do they say? Grohe makes a bunch of rough-in valves (1/2"-3/4", with varying flow rates). Which one do you have (model number)?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    "...are you going to use a divertor in the tub filler spout, or a separate valve?"

    Separate Valve -- there is no diverter in the tub spout that was purchased.

    Model Number 34-122 1/2" thermostatic valve....

    I get what you are saying, but it still seems like it's more complicated than it should be. Why can't I come off the top and the bottom with in-line volume controls to the shower and the tub? The included instructions don't really cover what should go where. There is limited text and some pictures that don't really show how to install this valve in a tub/shower application. There is a picture of the shower only application, but that is a no brainer (cap the bottom -- in line volume control). Further, the pictures show the installation for the individual components with little reference to the other components that must be installed with it -- hence my confusion.

    I did do some more research online and saw that there may be some temperature variance if both the top and bottom outlets are used simultaneously. Why manufacture it with two outlets then, if you always have to cap one?

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    My guess is that you can use two separate volume controls, one off each outlet. You might want to give them a call, or if not them directly, check for their nearest distributor. If you opened both valves, though, with the restrictor in the showerhead and the difference in height, you probably wouldn't get much out of the shower.
    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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