Clogged KWC shower mixing valves

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by Matthias, Sep 28, 2012.

  1. Matthias

    Matthias New Member

    Messages:
    9
    Location:
    San Francisco
    I have a problem with rust (I think) and other stuff clogging the screen (or is it a filter?) of my KWC shower mixing valves. See attached pictures. For the past 6 years since I installed the valves, I have had to clean them out every 3 months or so because hardly any water came out the shower head. And as of this summer, I have to clean them every 4 weeks. The picture shows one screen the way it looks after just 4 weeks, the other one is clean after I remove the gunk with a tooth brush.

    My question(s): What is that stuff that collects in the screens? The brown stuff is almost slimy. I assume it's rust, but where would it come from? My house is connected to city water. Most of the pipes are copper, except for one bathroom that is unused. Landscape pipes are partially old rusted galvanized, but there is a backflow preventer that stops rusty water from flowing into the house. What is the white and the green chunky stuff? the white stuff feels greasy.

    Any ideas? I'm getting tired of disassembling the valves and clean them out so frequently...

    Thank you,

    Matthias

    IMG_20120926_195720_s.jpg
  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,001
    Location:
    Bothell, Washington
    Is it on both the hot and the cold side?
    If it's only the hot side, then I would factor in the water heater.
  3. Matthias

    Matthias New Member

    Messages:
    9
    Location:
    San Francisco
    It is both on the cold and hot side. The water heater is a tankless heater that is 8 years old. I recently had that serviced. It has it's own screen, which is much coarser. I did not see any of the brown stuff in there since the screen has bigger holes, but a large clot of the white stuff. The white clot was greasy, almost like soap scum.

    Thanks,

    Matthias
  4. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,618
    Location:
    Cave Creek, Arizona
    How do you know it is both the hot and cold side? They both flow into the shower head so either one, or both, of them could be the cause of the problem and your symptoms would be EXACTLY the same.
  5. Matthias

    Matthias New Member

    Messages:
    9
    Location:
    San Francisco
    The mixing valve has a separate screen for both the cold and the hot water pipe before the water goes into the thermostatic mixer. The schematic drawing for the valve is here:

    http://www.kwcamerica.com/doc/technical/archive/KWC_THERM_802516.pdf

    On page 2 on the right you can see the place for the two "pre-stopper" units, one for the cold inlet, the second for the hot inlet. They contain the screens that I show on the picture in the initial message. Both of the screens are equally dirty when I take it apart to clean.

    Matthias
  6. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,618
    Location:
    Cave Creek, Arizona
    You have an interesting problem, because any sediment in the cold water piping would "precipitate" out of the water in the water heater's tank. If it is originating in the water heater, then there should be none in the cold piping.
    Last edited: Sep 29, 2012
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,995
    Location:
    New England
    I'm wondering if it might be biological...

    Does it dissolve if you put those screens in some vinegar overnight? What about any changes if you soak it in some bleach? Does the color change as it dries?
  8. jkubby

    jkubby New Member

    Messages:
    1
    Location:
    Santa Cruz, California
    Slimy stuff in the pre-filter to my tankless hot water heater

    I have a similar problem with clogging in the pre-filter to my tankless hot water heater. The problem just started a few months ago after years of problem free operation. The screen pre-filter gets clogged on a weekly basis by this brown slimy stuff. Sometime it clogs slowly and sometimes it clogs suddenly, leaving me wet in the shower with only cold water. Not fun! There is an Aqua-Pure filter (AP431) in front of the tankless pre-filter which is supposed to reduce scale. Somehow the brown slimy stuff makes it through the Aqua-Pure filter and gets stuck in the screen pre-filter. I have tried changing out the Aqua-Pure filter several times to see if that is where the brown slimy stuff is coming from, but no luck. I am on well water and there is a large paper filter between the pump and the house to clean out dirt from the pump. I change out that filter every 6 months. Any ideas where this brown slimy stuff could be coming from? I have run the water going to the tankless out to a drain for a long time to try to clear the lines, but that doesn't seem to do it. I think I may have alien life forms living in my plumbing!!!! HELP!!!!!!!!


  9. pbinCA

    pbinCA New Member

    Messages:
    1
    Location:
    Pleasanton CA
    Brown slime

    I use a Franke water filter for drinking an cooking water. When I take out the filter element, it is covered with brown slime. These reflect two different things in the water:
    Rust - reddish brown color - ferric oxide - rust originating in steel piping
    Clear slime - proteanacious material from upstream lifeforms - they concentrate at the filter, but are very dilute in the water supply


    Other things you might see:
    Turqoise stuff - copper oxide - natural rust color of copper
    White solid - scale, or calcium carbonate - natural mineral from well water that comes out of solution and grows into solid chunk

    If you understand your plumbing, there may be a way to backflush your shower filter. It requires applying water pressure backwards to the filter, and opening a faucet somewhere nearby so the crud will flow into a sink drain.

    I discovered backflushing many year ago when the bath hot water flow rate was getting very weak compared to the cold flow rate.
    It's due to rust buildup at the bathtub mixer's HW intlet.

    Once a year I backflush the bathtub mixer valve using this method:
    1. Shut off HW supply pressure at the hot water heater tank
    2. Open the HOT sink faucet near the bathtub (no flow since HW supply is off)
    3. Start the bath filling with a medium temp. setting (equal hot and cold) - shower diverter should be OFF!!
    4. Cold rusty water now comes out of the sink faucet....this is the crud that was stuck at the bath/shower mixer.
    5. When the rust clears, you restore HotWater pressure at the heater tank. That's it.

    How does this work? You have to imagine what's going on behind the shower wall. When I start up the bath, the mixer is only getting pressure on the COLD inlet. Because I've opened the Hot Faucet at the sink, I've created a path for cold water to flow there via the bath mixer....cold water flows backwards through the mixer's hot inlet. Backflushing!!!
  10. David Walker

    David Walker New Member

    Messages:
    1
    I realize this is a very old post, but in the desperate hope that someone is monitoring it, I have a question. Referring to Matthias's original post, how does one get at the filters that he provided a picture of? I have removed my KWC shower cartridge and put it in vinegar. No luck. My original symptoms: When I first bought our house in February, I noticed that when you turn the the temperature dial to hot, the pressure was low, but usable. Now, however, it's barely a trickle. I wrote to KWC and they said to simply remove the cartridge and then turn the water back on. This will apparently flush the system. I did this but no luck. I see that folks mention filters. Can the cartridge be disassembled and the filters cleaned? Can someone provide detailed directions and/or links?
  11. Matthias

    Matthias New Member

    Messages:
    9
    Location:
    San Francisco
    David, you need to unscrew the "stop valves" (refer to the PDF I provided above, http://www.kwcamerica.com/doc/technical/archive/KWC_THERM_802516.pdf). Those come out using a 3/4 wrench. Then, on the back side of each stop valve you see a pin, maybe 3/8" diameter. Gently pull that out and you'll find the sieve underneath it. I can easily be removed and cleaned.

    Hope this helps.
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