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Wildly erratic temperature readings from ecobee Smart Si!

scottkeenscottkeen Member
edited July 2015 in ecobee

I've had a total of 3 ecobee Smart Si units. The first one works great, no need to talk about it.

The 2nd one was giving me wildly erratic temperature readings. Even playing with the offset, I would get erratic numbers. By comparison, my old OEM thermostat sitting right next to the ecobee would consistently show the correct temperature while the ecobee would show anywhere from +2 to +9 degrees off. It's the summer, so not sure what it would do in the wintertime, my guess is the same in reverse. If my OEM thermostat showed "68 degrees", the ecobee mounted right next to the OEM unit would show anything from "72" to "75" degrees. I'd have the Cool setting set to "70 degrees" and the ecobee would be cranking all day long trying to get there, always stuck between 72-75 degrees and meanwhile it's freezing in my house at 66 degrees.

I exchanged this unit for another unit with ecobee.

Same exact problem on the 3rd unit.

So, I don't know what to make of this. Do I have the equpment selected wrong? Would that make a difference? What would be causing this? My only guess is it's defective.


  • MooseMoose CanadaMember
    edited December 2015

    I had the same problem with the SMART thermostat. Replaced on warranty, issue remained. Turned out to be a problem of the internal circuitry heating the sensor slightly.
    When the fan came on, the air circulation in the house increased and the sensor reading would change to "normal", dropping at least 1-2 C below the 1st-stage threshold. When fan turned off, the sensor reading would increase again. As a result, I experienced wide temperature swings during heat mode.
    I solved it by adding an external sensor connected to the add-on sensor board. The external sensor is placed just below the SMART and works perfectly.

    From your pictures above it could be that the air vents in the Smart Si are blocked...

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