Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Mixing valve malfunction?

RyanW Member Posts: 31
I am in the process of installing my new  drain back solar hot water system that many of you gave great advice on during the design stage.   I used this project as an excuse to re-do the plumbing layout in my tiny utility closet and in the re-design I have added a thermostatic mixing valve per code.   Last night I finally turned the water back on and encountered an unexpected result.   The mixing valve is a honeywell AM101-US-1 which all of the local solar  installers seem to use.  It is installed to temper both the solar hot water and the water that comes from my backup on demand heater.   As the solar is not yet hooked up it is currently only tempering the on-demand heater.    The problem that I encountered  is that so much water flows through the cold port of the mixing valve when I turned the tap on that the on-demand did not even kick on.   I noticed that the valve was set at the coldest setting so I re-adjusted the valve to the hottest stetting 145* and so the demand heater kicks on but the valve still mixes in cold water.   It tempers 140* down to 120* and the  120* water down to 110*.     If I shut the ball valve to the hot water heater I can still get about 1.5gpm of pure cold water from the tap which is only flowing through the cold port of the tempering valve.    

Is this normal?   I was under the impression that the tempering valve would only add cold when the incoming fluid got above the set temperature rather than always adding cold water.    I don't like the idea of it always tempering the water and also giving inconsistent output tmperatures.   The valve is brand new! 


  • hot_rod
    hot_rod Member Posts: 22,113
    thermostatics and

    on demand tankless type heaters don't always get along so well.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Fortunat
    Fortunat Member Posts: 103
    sounds like

    sounds like a bad mixing valve to me.

    If it is set to 120, it should stay at 120 (plus or minus a couple degrees) whether you feed it 120 or 150 on the hot side.

    We had a whole batch (maybe 6 or 10) bad Honeywell AM-1 mixing valves about 18 months ago (though in that case the failure mode was worse because they failed open to HOT). We sent them back and they were replaced by our vendor under warranty, but we never did hear any update on what went wrong.

    We've since been using the Caleffi's and have had better luck with them.


  • RyanW
    RyanW Member Posts: 31
    More data

    It seems like it wants to temper all of the water down by 10 degrees.   The photos that I posted in the first post were with the termostat set at a full 145 max.   I did some more tests this evening with one sink running a full 2.5gpm full hot flow.   I messed around with the dial until the outgoing temp was 120 degrees.   It kept a constant 120 output when the incoming water was 150, 140, 130 degrees.   BUT when I lowered the incoming water to the same setting of 120 degrees it lowered the output to 110!    Seems like a lemon to me or is this normal tempering valve action?

    I just don't want to get into a position of having 110 degree solar water tempered down to 100 or less and thus force me to have to turn on the back up heat.   I thought that they would not add any cold water unless the incoming water temperature was ABOVE the set outgoing temperature.  

    I bought this one as the supplier that I was working with had them in stock at a great price and now I wish that I had tried the Caleffi instead.    Will it give me the same results though?   And do they fit the same unions or would I have to sweat some new ones on? 

  • hot_rod
    hot_rod Member Posts: 22,113
    make sure of the inlet conditions

    you need to assure the inlet cold and hot are within the requirements of the valve. Not all mix valves are required to fail "cold" it depends what listing they are built to meet 1070, 1017, etc.

    The problem that I have heard with tankless is the valve may not respond as quickly as the temperature from the heater, it could then fall outside of what the valve was intended to compensate for.

    Notice the pressure and temperature requirements of this valve. Does it have check valves installed? Could hot water be pushing back the cold side?

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    They aren't perfect

    The Honeywell will always leak some cold water through, no matter what the settings and inlet temperatures are.  Due to manufacturing tolerances, it doesn't seal off the cold side 100%.

    You will see more of the cooling effect at lower flow rates.  So yeah, what you're seeing is normal for that valve.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • RyanW
    RyanW Member Posts: 31
    is there a better valve?

    So is there a valve that will not bleed cold in on a regular basis?   We often us a low flow for dish washing and the dramatically lowered temp is a annoying.   I would love one that only lets cold in once the incoming temp raises above the set temp on the valve.   Perhaps impossible?

  • RyanW
    RyanW Member Posts: 31
    Caleffi thermosats work better!

    I picked up a Caleffi 521 valve to try in my system.   It does have the same union fittings as the Honeywell so switching them out was a cinch.    It works perfectly! With it set at 120* when I feed 140*, 130* 120* from my on demand I get 120*, 120*, 120* respectively.   There could be a 1* cold bleed but It was not noticeable on the thermometers.   Over two weeks of testing with the Honeywell I got a consistant 8-10* temp drop from cold bleeding!   Thus with it set at 120* with 120* feeding it I would get 110* output.    Anyone want a used Honeywell tempering valve?

    Thanks All.

  • Steve Fontas
    Steve Fontas Member Posts: 26
    Kevin is right

    Expect a near constant 10 degree drop with the Honeywell valves...
  • Royboy
    Royboy Member Posts: 223
    edited June 2011
    similar issue

    I ended up having Honeywell send me 100-145° replacement cores for 24 AM1 mixers to replace the original 80-120° cores. no way that I could get them to put out consistent 120° water with the original cores - more like 115° and that was not acceptable to me or the client.

    just returned all my honeywells to supplier and will try caleffi now. slightly pricier but if they work I will be a happy convert.

    hr - what's the diff between the caleffi 521 series and the 252 series (solar line) besides the color of the knob? the specs look pretty much the same at first glance.
This discussion has been closed.