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Aquastat problem, question

Thanks to all for the suggestions & input. Let me just clarify that my main concern is about using extra oil ($) to keep my boiler temp any higher than I absolutely need to.

I've always kept my Aquastat set to 180/160/15diff, and up until recently the burner & circ always kicked on/off at all the correct temps (according to the boiler temp gauge, anyway). I recently installed a new h/w coil too; so I was getting plenty of hot water with the boiler btwn 180 & 160.

Until I have the time to really check things out, I tweaked the Aquastat's Hi & Low limit settings so that everything works "correctly" according to the thermometer. For now I'm going to assume that the thermometer is accurate, and that the Aquastat bulb is somehow reading about 10-20* too low (possibly because of scale buildup on the immersion well?)

Once I have a few spare hours, I'll pull the bulb, well, and thermometer/pressure gauge assy so I can clean & test everything. I should be able to test the Aquastat using a continuity meter, a known-good thermometer, and some hot water.

I'll keep everyone "posted" ...

thanks again,


  • johnnyzero
    johnnyzero Member Posts: 7
    Aquastat problem, question...

    I have the High Limit on my Honeywell L8124A set to 180*, but burner cutoff doesn't happen until about 200*.

    Before I replace the Aquastat ****'y, I wanted to see if anyone thinks this might be caused by scale buildup on the "wet" side of the immersion well. I'm thinking that the scale might be acting as an insulator between the boiler water & the well, and therefore throwing off the bulb's temp reading. Does this sound likely? If so, I'll go ahead and pull the immersion well and clean it with some LimeAway or whatever.

    (I haven't had a chance yet to check whether the Low Cutoff is "off" by a similar amount, but that would certainly confirm the "scale" theory)

    Also, what would you guys recommend using for my Hi/Low/Diff settings? I have an oil-fired burner with tankless water heater. It's a small two-story house, 2 baseboard zones w/ zone valves, and a single circulator for both zones. With oil prices so high, I really wanna try to max our efficiency this winter!

  • bigugh_4
    bigugh_4 Member Posts: 406

    !. If you try the high off setting once a month and it goes off at 200*F each time I'd leave well enough alone
    2.You must be reading the temp somewhere else as the aqua stat has no reading of temp upon it (except hand wheels). Therefore you are comparaing two thermometers. The aquastat AND a readable thermometer. The aqua stat is lots more expensive than the .05 &.10 (five and dime) readable thermometers. Take your pick and use the one you want to believe. The temp is 90% correct, at this point anyhow.
    3.If you are really interested about the Temp and the diff setting, you can get solid state equiptment that can get to within one degree on<>off.
    You could get ( or borrow) a infeared thermometer if you wanted another Thermometer's guess as to what your boiler is really set at.
    Its all a scientific wild **** guess anyway!
  • Al Letellier_9
    Al Letellier_9 Member Posts: 929

    I would think that you are reading the temp gauge on the boiler? I would trust the aquastat first. Boiler gauges are notoriously way off, especially as they get older. cleaning the well is never a bad thing, but may not be necessary. As to the settings, depending on where you live and how much temp your system needs, you set the high/low 20 degress apart. Here in Maine, the norm is HI 200/LO 180 with the differential at 20. That give the boiler longer run cycles on domestic hot water call and longer draw down before the burner activates. Good luck

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