Question about Grohe Plumbing

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I have no hot water coming out of a shower with a Grohe 2 part control. One controls volume, the other controls temperature. I tried installing a new temp. control valve, but there was no difference. I then removed it and ran the water without the temperature control valve in place and only cold water flowed out. It's in an older home with the possibility of galvanized pipes being clogged, but there is plenty of hot water coming through the sink. The mixing valve is behind a tile wall. Do you have any suggestions before I have to remove some tile?

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  • kbizzarro Sep 09, 2010

    Thanks for your suggestion. I'll give it a try. I just have to figure out how to get that compressed air from my compressor with any pressure into the shower control opening. If I take the control valve out ( which operates the temperature and flow control through an approx. 1 1/2" opening) it will be difficult to seal. I will try sending it back through the shower head supply tube and see if I can get some air pressure to blow back through the sink.

  • kbizzarro Sep 11, 2010

    I tried your suggestion, but unfortunately, it didn't clear the line enough to make a difference. I got some limited blow back through the sink supply tube, but not enough to make a difference after repeatedly trying compression and decompressing the line with 120#s of air pressure. I ended up removing some wall tile and found copper feeds to the mixing valve, but unfortunately I suspect that there may be galvanized pipe in the floor between the sink and shower. Access to this section to verify will involve either ripping out a tile mud floor, or from underside ceiling exposure from a very large formal living room.
    Someone had renovated this bathroom previously, but unfortunately they probably didn't do a complete overhaul of the ancient plumbing. I need Superman with his X-ray vision for this one!

  • kbizzarro Sep 11, 2010

    There is only one exterior on/off water control with a water temperature dial attached to the same arm.
    There is no way to turn only the hot side on by itself. I blew compressed air back through the shower head arm,trying to clear any possible blockage, removed the supply tube under the sink and still pushed back very limited pressure after fully opening the shower control set on 110 degrees ( it's highest dial temp). After opening a wall section, I found copper supply tubes to the shower control valve, but I suspect that they are fed by a galvanized feed after the sink and back to the shower.



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Your description indicates that it is indeed the mixing valve (tempering valve) that is at issue.

There are a few things that you can try, depending on how far you want to go. By default, the mixing valve will go to "full hot" once it detects water temperature has dropped below its set point. If you have even a trickle of water when turned to full hot, then you may be able to pump a weak acid through the hot water pipe (break apart a union that feeds only the shower), and the acid may clean out the build up. This probably won't work since only the cold side is flowing.

Before removing tile, consider accessing it from the other side of the wall, through plaster / drywall. Once repair is done, hide the access panel using a picture / frame or some other method.

Posted on Sep 10, 2010

  • Sheldon Dedek Sep 12, 2010

    I saw your comments in response to other solutions, and have a suggestion to add to the compressed air idea.

    If there is a restriction in the pipe that runs in the floor, the air may be whistling by it, making noise. If you are able to use a long hose between the compressor and the shower head, you can make it relatively quiet in the bath area.

    When the air is blowing back through the sink, use a "Super Ear" or similar type of amplifier to see if you can trace the flow of air from the sink back to the shower. When you come across a "noisy" area, mark it. Trace back from shower to the sink, and see if the previous marked area is the noisiest spot.

    If it is, that is likely where your obstruction is located. I may not be superman, but with a child's toy, you can have Super-Hearing.


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Before removing tile I would shut the hot water off and then open the hot on the sink... then blow compressed air backwards through the hot pipe and see if you can get the dirt to back probably have rust built up in there and maybe if you can blow it back and out the sink it will work for you....
Remember is take the aerator off of the sink so that the **** can come out there....or better yet take the supply tube off at the sink and let the air blow out there so you don't run the risk of plugging the sink faucet up...


Posted on Sep 09, 2010


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