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mixing valve issues

I installed a mixing valve in my grandparents house. The domestic hot water is heated in the boiler i believe it has a small reserve tank inside. The valve is located a few feet above the boiler with no thermal trap.  My problem is that the hot water coming out at the fixtures only comes out for a short period. Much shorter than when there was no mixing valve. will a thermal trap fix this problem?


  • billtwocase
    billtwocase Member Posts: 2,385

    the trap will help to prolong the life of the internal element. Sounds like you need a flow restrictor, or a new coil. What temp is it maintaining?  Pics?
  • Zman
    Zman Member Posts: 7,579
    cross connect

    Do you have a flow check between hot and cold.?

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • icesailor
    icesailor Member Posts: 7,265
    Cold Mixing

    You could have already had the element fail if the valve is installed (incorrectly) over the top of the boiler or above the cold water inlet of the coil. It is spelled out emphatically in the provided instructions that no one ever reads. But on a Massachusetts Journeymans exam, if you don't show the heat trap, you get the question wrong.

    When they get cold right away, the element is usually gone. If you slow the hot water down to a very low flow and you still have hot water, you need a flow restrictor. If it is a new boiler, the installation manual will tell you what size for your particular boiler. If it is old, it may need the coil cleaned.
  • layin_pipe
    layin_pipe Member Posts: 2
    its not themixing valve

    after further investigation the water is hot for a minute or two and then it gets cooler at the faucet. after running the water till it was cool i checked the water coming directly out of the coil before the mixing valve and it is luke warm.  will cleaning the coil help? i was thinking about an electric water heater instead of replacing the coil
  • icesailor
    icesailor Member Posts: 7,265
    Hot Water:

    Does the burner or heat generating source start shortly after you turn on the hot water?

    What kind of appliance is providing the heat input? Gas or oil?

    If oil, what are the control settings set at?

    The coil may be dirty but the element in the mixer may be burned out because the instructions show that it MUST be installed 8" to 12" BELOW the cold water inlet to the coil to stop heat circulation and burning out the element in the valve. If the valve element is broken, it can by-pass the coil altogether and let a minimal amount of hot water through the defective valve.

    Need more information.
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