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mixing valve piping

Fizz Member Posts: 547

Had boiler serviced today, and pointed-out the corosion on mixing valve pipes and supplies to tankless heating ports. Was told I need new valve as old one is ball and doesn't meet codes and curent temp control allows water to reach scalding temps during heating cycle. Your input is appreciated. Thanks, Fizz


  • Jamie Hall
    Jamie Hall Member Posts: 20,404
    Quite right. If you do make any repairs -- though if it's not really leaking, I'd leave it alone -- you do need a thermostatic mixing valve, not a fixed valve like that ball valve. It would involve minor repiping. The arrangement you have could indeed reach scalding temperatures (particularly since that mixing valve is almost closed) when the boiler is actively steaming.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ethicalpaul
    ethicalpaul Member Posts: 4,174
    My old house had a mixing valve but it seemingly failed to allow too-hot water. I cut the pipes off the coil and installed a resistive electric water heater. They only cost about $500/year to operate and you don't have to heat up a whole boiler and your basement all summer to take a shower.

    Today of course I would install a heat pump water heater since those cost pennies per day
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
  • Fizz
    Fizz Member Posts: 547
    Thanks guys. Yes Jamie, no leak, and I love the hot water, no kids here. Are thermostatic mixing valves dependable?
  • hot_rod
    hot_rod Member Posts: 18,177
    The dependability of any valve is dependent on the quality of the water flowing through it. Also how much water it sees passing through

    Hard water, high mineral content is tough on mixing valves. In some cases a yearly cleaning and declining may be required.

     A Caleffi 520 AngleMix is an excellent valve for tankless coils or tankless heaters A quick responding valve with scald protection, it will close off if it loses cold supply.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EBEBRATT-Ed Member Posts: 13,089

    I would follow @hot_rod direction

    Just make sure the installer follows the install instructions. Some valves need to be trapped
  • Fizz
    Fizz Member Posts: 547
    Great advice, thanks.
  • Fizz
    Fizz Member Posts: 547
    Addendum to original post: the boiler is a 26yr old SGO 3, which performs well with an 81% efficiency, so I'm reluctant to spend a great bit of $ on any upgrades.