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Boilermate mechanical thermostat

I just added a Caleffi thermostatic mixing valve to my 41 gallon Amtrol boilermate indirect tank. I've heard stories of the these tanks becoming damaged if they are run too hot. Unfortunately I have the mechanical aquastat on mine, there is a spot on it marked for 120 degrees and the Amtrol specifications say the maximum working temperature is 150 degrees.  I have temperature gauges on the boiler piping to the coil and on the mixed hot water out of thermostatic mixing valve, but I have no way to know the temperature inside the tank. Currently the aquastat is set to 5, the highest setting is 6. Does anybody have any idea how hot the temperature might be inside the tank at this setting?


  • Zman
    Zman Member Posts: 7,605
    I think that high temp is just an excuse for failure of a poorly designed product.
    Boilermates have issues with undersized heat exchangers, heat exchanger scaling, leaky heat exchanger gaskets and tank failures. I do kind of like the color though. :D
    As for the aquastat, you could pull the probe when the aquastat is satisfied and measure the tank temp with a digital sensor. One would hope that if Amtrol insists on installing a cryptic aquastat on their tank, it would be designed so you cannot exceed max tank temp.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • SuperTech
    SuperTech Member Posts: 2,205
    edited September 2020
    @Zman Thank you, thats probably what I will have to do to check the tank temperature. Unfortunately I have the boilermate with everything on the bottom. I suppose I could install a temperature gauge between the tank and mixing valve as a way to check temperature. 

    Does anyone think its safe to assume that 150 degrees is the maximum setting of the mechanical aquastat since Amtrol specifies that is the maximum operating temperature?

    I don't consider the boilermate to be a bad product, don't see a lot of problems with them in my area. Mine was producing 110 degrees hot water before the first burner cycle after i refilled it. I saw about a 40 degree delta T on the coil.  

    I have Buderus indirect with a pinhole in the coil that I'm going to use for a Buffer tank. I can definitely see a difference in the quality of the design.  But I'm sure it cost as much as two Boilermates when it was new.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    I'd be more concerned with the composite buffer tanks for temperature. But if you're 150° at the bottom, what are you at the top?
    You have your mixing valve on the domestic side, not and additional one the boiler side feeding the tank?
    I notice on my indirect, the boiler is almost never sending 180° to the tank, with a pretty high delta T.

    There was an error rendering this rich post.

  • rick in Alaska
    rick in Alaska Member Posts: 1,458
    Personally, I would not worry about it. Like all controls, it can fail and over heat the tank, but doesn't happen often. Just be glad you don't have the digital stat. They are prone to failure. And as far as the tank goes, it all depends on your area, and water quality. I have only had problems with four of them, and three of them were because of the digital aquastat failing, and the other one was because of severe water hammer.
  • SuperTech
    SuperTech Member Posts: 2,205
    I've run into the digital aquastat failures once or twice. It looks like i check the temperature at the bottom of the tank by pulling the sensor for the aquastat, I can check the hot water pipe into the mixing valve with the clamp on thermocouple for my multimeter.  That should give me an idea of what the tank temperature is. 

    @STEVEusaPA i have an outdoor reset module for my L7224U aquastat on the boiler,  it includes a sensor for the indirect tank so it can override the ODR and run the boiler to the high limit for fast recovery.  After seeing how fast the tank recovers I might drop the high limit down a bit. Mixing is done by variable speed injection.  The Buderus indirect tank that I will be using for a buffer tank isn't a composite like the boilermate.  
  • clammy
    clammy Member Posts: 3,113
    I ve had both boilermate mechanical and electronic controllers fail over the years and over the past 10 years or so I ve been replacing them using ranco etd . They where cheaper then Oem and have a setable differential and have a keypad lock out . I ve yet to have the ranco fail ,I also strictly use the 110 volt models I stay away from the 24 v ones just one more thing to add or have fail . They aren’t the worse tank and the only failures I ve dealt w where due to high pressure house water pressure and no domestic expansion tank . With the bottom mounted coil they do lime up but if provision are piped there pretty easy to de lime At least I ve had pretty good luck on the few I ve done. Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating