Moentrol 3520 "hot water"/"cold water" mixing problem

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by rebarman, Dec 25, 2019.

  1. rebarman

    rebarman New Member

    Joined:
    Nov 29, 2014
    Location:
    California
    I searched quite a bit in the forum and even though I see a lot of moentrol questions, I don't see the issue that I seem to be having. Sorry in advance if this is a repeat!

    I have the moentrol 3520 mixing valve. It was installed years ago but almost never used, but now it's in regular use and is showing this issue where I can get cold or hot water but only after a lot of fiddling can I get warm water, which is the goal.

    my description:
    I turn on full hot to start, and once the water is hot I start moving the lever towards cold to get to warm, but there is no reaction (stays hot) until the lever is way over to the cold side, then the water gets too cold and there is a slight "clang" sound coming from the valve. So I try to go toward the hot side again, but in the same way there's no reaction until it gets too hot. Then the cycle repeats and I start going back toward the cold side again trying to get warm water. Eventually, I can get it to be warm, but there's too much water wasted and a bit of frustration.

    I put in a new moen cartridge, but nothing changed.

    I saw one thread where Terry posted a cutaway of the same valve that I have. I didn't realized there was another replaceable part, the Pressure-Balancing Spool. Could this be where the problem is?

    I'd like to see a video showing how these valves work.

    Thanks for any help that you can offer!
     
  2. rebarman

    rebarman New Member

    Joined:
    Nov 29, 2014
    Location:
    California
    I found this thread that I think answers my question with a lot of tips and pictures, and points out that the pressure balancing spools can stick in a shower that doesn't get regular use. Exactly my situation, except mine doesn't stick completely! And it eventually works once it's lubricated by the water. Going to clean it up and guessing that will take care of it! great forum!

    https://terrylove.com/forums/index.php?threads/moentrol-3285-no-cold-water.8971/
     
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