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Aquastat problem, question

Get actual line temp on supply side before going into panic mode. Aquistats are somewhat accurate, but not a labratory control. As long as you know what the temp is, don't worry about it. From above the guage could be off also.


  • johnnyzero
    johnnyzero Member Posts: 7
    Aquastat problem, question

    (after posting this msg to The Wall, I saw that there was another forum specifically for questions about controls, so I've posted it here as well)

    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!

    thanks, JohnB
  • Rookie_3
    Rookie_3 Member Posts: 244

    Don't rule out the boiler guage being the faulty source. See what you read on the low limit temp. to see how acuate that is to the aquastat. I like 20 for a dif., some come with a fixed 10..............ROOKIE
  • darin_2
    darin_2 Member Posts: 12

    Mike T gave good advice. Relax the water won't turn to steam at 12 psi until over 230*(I don't know the exact number, sorry). It's not worth worrying about.
  • johnnyzero
    johnnyzero Member Posts: 7

    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,
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