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Buderus indirect hot water tank temp sensor

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RickW
RickW Member Posts: 3
in Domestic Hot Water
I am using a Buderus 160/1 indirect hot water tank. I have the Logomatic DHW temp setting at 130°. Lately the water has been scaulding hot. I am guessing the temp sensor is bad but, in lieu of just replacing parts, does anyone know the normal ohm values for this sensor? Note, I am not getting any error codes on the display
Thank you

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  • HVACNUT
    HVACNUT Member Posts: 5,835
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    Page 58
    mattmia2Alan (California Radiant) Forbes
  • Alan (California Radiant) Forbes
    Alan (California Radiant) Forbes Member Posts: 4,002
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    I've seen 10K and 20K sensors, but this looks like a 1.5K sensor, no?

    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
  • mattmia2
    mattmia2 Member Posts: 9,639
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    Looks like 12k to me. Typically the resistance of a thermistor is specified at 25 c however there are a could other parameters you need to be able to calculate its resistance at any other temperature. There are dozens if not hundreds of types of thermistors with different curves.
  • RickW
    RickW Member Posts: 3
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    Thank you HVACNUT, Alan, and Mattmia2

    If the chart shown is correct (I found the same chart in the service manual) at 190° I measued 1.89 ohms. So I guess I remove the sensor from the tank, let is cool down, and remeasure. If okay, then back to the drawing board ...
  • mattmia2
    mattmia2 Member Posts: 9,639
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    According to the chart at 190 degrees F it should be a little over 1 k ohm.
  • RickW
    RickW Member Posts: 3
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    Thank you, Mattmia2 yes I should have mentioned kiloohms. Turns out I read the wrong sensor. The dhw sensor "FB" according to the manual, read 2.76kohms

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