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Mixing valve

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icy78
icy78 Member Posts: 404
So per the drawing.
Is it probable that when the floor Loop pump is off , that the other pump can force hot water through the mixing valve and into the floor Loop? That is what I am seeing on site. I guess maybe this heat exchanger is restricted so that it's easier for the water to go the other way?
Or if that would be typical and actually that in-floor Loop may need a zone valve on it?
Or is that a malfunctioning mixing valve?

I verified that with the floor Loop pump off and the other pump still running, I saw temperatures as high as the boiler Supply temperature so at one point it was 156. That would be with my strap-on pipe thermometer at the manifold entering the floor , so a good six feet from the pump and it happens in, oh maybe 10 seconds it'll run up from 110 to whatever boiler Outlet temperature is it that time.

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  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    edited April 2019
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    I'd guess bad mixing valve. Seems like that's a long way to go instead of thru the hx and back to the boiler.
    Is your return from the radiant loop back to the boiler heating up?
    How about just an internal flow check (or a regular flow check) on the radiant loop circ?

    There was an error rendering this rich post.

  • hot_rod
    hot_rod Member Posts: 22,258
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    Do you have check tailpieces on the mix valve? Or a check in the radiant circulator. A gauge on the radiant circuit would indicate unwanted flow when it is not powered.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Intplm.
    Intplm. Member Posts: 2,006
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    If I'm not mistaken , I believe that mixing valve has strainers and check valves built in to it. There could be some debris stuck in the path of water flow allowing water to pass where it's not wanted.
    Undo the unions on that valve and rinse the strainer screens and the checks. That might fix the problem.
    If that doesn't correct the issue. Rebuild or replace it.
  • icy78
    icy78 Member Posts: 404
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    > @Intplm. said:
    > If I'm not mistaken , I believe that mixing valve has strainers and check valves built in to it. There could be some debris stuck in the path of water flow allowing water to pass where it's not wanted.
    > Undo the unions on that valve and rinse the strainer screens and the checks. That might fix the problem.
    > If that doesn't correct the issue. Rebuild or replace it.

    Well I forgot to mention that I did actually pull the mixing valve out. It's been in for approximately 15 years.

    There were no checks on either side.
  • Intplm.
    Intplm. Member Posts: 2,006
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    After posting my response. I looked on the Apollo website. Seems the "new" valve has checks and screens integral with the mixing valve. Didn't know about the ones fifteen years ago.
    If the valve is that old, and is having trouble maintaining a constant temperature (swings from high to low temps without stabilizing.)
    It may just be that valve.
  • icy78
    icy78 Member Posts: 404
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    > @hot_rod said:
    > Do you have check tailpieces on the mix valve? Or a check in the radiant circulator. A gauge on the radiant circuit would indicate unwanted flow when it is not powered.

    The intruding flow would be the same direction as the circ would pump tho. I don't see how a check would help because the hot is flowing thru the MV in the right direction but at the wrong time.

    Isn't there a song like that?

    musta been the right place , but it musta been the wrong time! 😀
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,622
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    Not sure if that is the best valve for the job and the way it is piped. Mixing valve is 2 ins and 1 out. so you have hot boiler water and cooler loop return water mixing in the valve to temper the loop supply. I get it. But the supply and return water are at 2 different pressures which I would think would make it difficult for the valve to control.

    I would take the mix valve out and leave the boiler water piped to make a crossover bridge into the system return & radiant return pipe. Then install the mix valve hot water in from the radiant pumped discharge. Mixed water to the radiant supply then put a tee in the radiant return and pipe it to the mixing valve cold.
    icy78
  • icy78
    icy78 Member Posts: 404
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    > @EBEBRATT-Ed said:
    > Not sure if that is the best valve for the job and the way it is piped. Mixing valve is 2 ins and 1 out. so you have hot boiler water and cooler loop return water mixing in the valve to temper the loop supply. I get it. But the supply and return water are at 2 different pressures which I would think would make it difficult for the valve to control.
    >
    > I would take the mix valve out and leave the boiler water piped to make a crossover bridge into the system return & radiant return pipe. Then install the mix valve hot water in from the radiant pumped discharge. Mixed water to the radiant supply then put a tee in the radiant return and pipe it to the mixing valve cold.

    Thanks for the info @EBEBRATT-Ed .
    Im lost on your how-to piping description however.
    The different pressures you mention make sense however.
    Any chance you could scribe a quick sketch?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,622
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    This will hydraulically isolate the radiant pump from the system pump
    icy78
  • icy78
    icy78 Member Posts: 404
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    > @EBEBRATT-Ed said:
    > This will hydraulically isolate the radiant pump from the system pump

    Are you saying possible BV due to the high flow resistance of the Htex? (Otherwise water may just want to bypass the Htex )?