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Water Heater & Mixing Valve controls

Our building has a Turbomax Instantaneous Indirect Water Heater that is tied into a hot water loop with our steam boiler. The cold water goes into the tank and comes out hot, and then through a mixing valve with a cold line before heating to apartments - I assume this is to regulate the hot water.

Now the Aquastat on the Water Heater is set to 125F. Is there any reason it should be higher?

My question is whether to tinker with the aquastat or adjust the mixing valve to get the appropriate hot water temperature. It seems boiler techs will come and turn the aquastat up or down which might have been because the mixing valve is faulty and they're trying to compensate? I see there's a temperature gauge right after the mixing valve - so I assume I want to make sure that temp is always above 120F. Which then I could either raise the Aquastat on the water heater or adjust the mixing valve to let less cold water in? Does this sound correct?


  • hot_rod
    hot_rod Member Posts: 19,923
    The aqua stat setting will regulate the recovery or production of the coils in the tank. The aqua stat will need to be set higher that the desired temperature to the system of course. Hotter tank produces more DHW draw. Often the tanks run 160- 180 to get maximum performance. The tank should have an output graph in the manual or online.

    The mixing valve regulates what the building sees.

    In some cases an addition point of use valve is added at sinks, etc for the extra protection, should the tank mix valve go bad or off.

    If you have a recirculation pump and loop there is a specific piping need to prevent thermostatic creep, or droop. The valve adjusts to provide exactly the amount of flow in the loop to overcome the heat loss in the piping.,
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • bcoyle
    bcoyle Member Posts: 29
    @hot_rod great info, thank you! - as I kept studying the setup it did occur to me that I'd want the tank to run a bit hotter/higher. I saw Legionnaires' disease as one reason to have the tank above 140F. Then of course you'd want to adjust the mixing valve until the water is more manageable, less scalding temp. I think around 125-130F is where the water temp is when reaching the kitchen/bathroom.

    My worry is that the tank isn't being maintained, nobody suggested replacing the air vent or cleaning it. Instead they want to install a new mixing valve.

  • hot_rod
    hot_rod Member Posts: 19,923
    looks like a lot of limescale in your water judging by the deposits on the air vent. The air vent is on the boiler side of the tank. Possibly a leak in the system allowing fresh water into the boiler?
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Lance
    Lance Member Posts: 248
    Bob Rohr knows what he is talking about. 95% of all DHW systems we see with recirc and mix valves are not right. When properly piped they actually work like they are supposed to. We are AO Smith tech reps for their products and commercial startups. Another flaw we see is the recirc pump flow is too high. Often a system is built to operate on timer or demand, but when put on constant waste energy and creates pinholes in pipes.
    Its a challenge to get it right in some mazes of pipes and controls we see. Like pumps put in backwards, check valves in wrong places, cross connections. All has to be right to work right. A great plumber is a noble creature. I just wish more would achieve greatness.
    HVACNUT Member Posts: 5,258
    I've only have experience with the smaller Turbo Max water heaters and that piping is not familiar to me.
    The "23" is 1 1/4 hot out the center top and to cold coming in from the bottom of the tank. What's the pipe behind the hot? Recirc?
    Like @hot_rod said, the air vent is on the boiler side. And so is that relief valve.
    Is there a domestic relief valve anywhere. I've seen many a Turbo Max piped without a domestic T&P relief valve.
    Back when I did installations I used a 1 1/4 x 3/4 x 3/4 tee on the hot with a 3/4F x street on the run out the top for the T&P.