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Funky indirect water heater...I'm scratchin my head

Andruid_2 Member Posts: 42
I need to know what's going on here.

I have an Amtrol Boilermate that's being heated by a Weil-McLain CGs Gold.  It's been there for Four years working just fine.  Customer calls up one day complains that the water out of her tap is "lukewarm".  I showed up and turned the dial up on the aquastat and everything hummed along just great.  Everything works the way it should.  Leave the dial a little higher than where I found it and explained everything works just fine.  Couple of weeks later ... lukewarm water.  I took an extra unused aquastat with me and replaced the old one.  Set the dial on 120 degrees and watched as everything cycled.  The aquastat's heat demand kicks out when the output at the top of the tank is at 115 degrees.  I cranked the aquastat all the way and it clicked off as the water temp at the top of the tank reached 120 degrees.  What can fool the aquastat into thinking the water is hotter than it really is?


  • False Reading

    The only thing I can think of is that there is a build-up of concretions on the aquastat well preventing the sensing bulb from reading the proper temperature.

    Can you remove the well and inspect it?
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • Andruid_2
    Andruid_2 Member Posts: 42
    False readings

    I can drain the tank and remove the well.  But I was thinking that scaling on the well would prevent the heat from reaching the sensor causing the boiler to keep pumping heat into it and causing an overheat situation... unless the scaling starts becoming hotter than the water for some reason.  Is there some reason that scaling on the sensor well would become hotter than the surrounding water?
  • SpeyFitter
    SpeyFitter Member Posts: 422
    other basic checks?

    First off - the obvious things - did you do a continuity test on the aquastat? Did you jumper the wires together to see if the boiler responds readily to this on/off signal ? Check the connections on the boiler side of the Aquastat wires? You have a reliable means to measure the actual tank temperature plus or minus a degree or 2? I'd definately check the well and if the tanks never been drained before now's the chance to do an annual or bi-annual sediment flush.

    I'm unfamiliar with this type of tank - there's not a dip tube is there?
    Class 'A' Gas Fitter - Certified Hydronic Systems Designer - Journeyman Plumber
  • Andruid_2
    Andruid_2 Member Posts: 42
    No dip tube

    The cold water enters at the bottom of the tank and exits at the top.  The well extends up from the bottom about 15 to 20 inches through the center of the spiral coil that also extends upward from the bottom.  Your absolutely right, I should do a sediment cleaning...it may even shed some much needed light on the situation.
  • Wayne Heid
    Wayne Heid Member Posts: 49
    Check the cold water inlet

    Some of the older Boilermate indirects were prone to losing the diffuser on the cold water inlet. This would cause the cold water to shoot up to the top of the heater and have the effect of tempering the hot water at the outlet. Much like a standard water heater with a missing dip tube.

    The "diffuser" was simply a 3/4" copper cap held by a small stainless steel screw. If the screw comes loose, the cap falls off and results in lukewarm water even though the controls say the tank is at set point.

    If you pull the coil you'll probably find the parts in the tank. Use some Loctite to secure the screw when you reassemble it.

    Hope this helps.

  • Chadio
    Chadio Member Posts: 4
    Outdoor Reset?

    Is the boiler firing on outdoor reset? If so, when the call for heat comes from the indirect, the boiler output may not be hot enough to produce effective heat transfer. 
  • Andruid_2
    Andruid_2 Member Posts: 42
    outdoor reset

    Yeah, it's on outdoor reset for the floor heat, but that's an injection loop.  The indirect loop is always high fire.
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