Moen Single Handle Shower/Tub valve problem

Discussion in 'Shower & Bathtub Forum & Blog' started by short.circuit, Apr 13, 2009.

  1. short.circuit

    short.circuit New Member

    Apr 13, 2009
    I installed this valve on a friends tub/shower in her basement.

    when we turn the hot water on, it comes out the spout just fine.
    if we turn some cold on with it, some water comes out of the shower.
    should we bug moen, about getting a replacement cartridge? or would that help?
    thanks in advance for any advice...

    here's a pic of the install...

    Attached Files:

    Last edited: Apr 14, 2009
  2. Redwood

    Redwood Master Plumber

    Dec 15, 2007
    Service Plumber
    No because it was piped incorrectly.
    Read carefully the instructions and you will see that you cannot run PEX to the tub spout.
    The slightly smaller size ID of the PEX creates just enough back pressure to cause water to rise up to the showerhead...

    Only copper or IPS pipe may be used here.

    Last edited by a moderator: Jul 21, 2017
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  4. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego, CA
    Apparently you missed the step in the installation instructions where it said to use ONLY copper pipe, NOT pex or cpvc, for the spout drop.
  5. short.circuit

    short.circuit New Member

    Apr 13, 2009
    fortunately it was a fiberglass, shower/tub surround. was able to remove the 1/2" male & dropear 90. i'm wondering if the pex pipe would work ok with sharkbite fittings. pex fittings look more restrictive. i was tempted, but went with copper & it works fine now. way more flow/pressure.
    lesson learned... thx again
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    You'd have had the same problem with PEX...the ID is smaller than copper.
  7. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    HOW you connected the PEX would not have made any difference. The problem was the PEX itself.
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