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Solved! Setting Run vs Hold on Trane TZEMT400 Thermostat

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  • Solved! Setting Run vs Hold on Trane TZEMT400 Thermostat

    This one has bugged me for many years… There's a hack to switch between ESM and Run/Hold, but the latter sets back to the most recently used of Run or Hold, whichever was most recently used; there's no way to force one or the other. If a user has set the thermostat locally to Hold, then that's where it stays.

    Inspired by jayph and his work deciphering the Trane XR524 (I didn't know you could read parameter values that way!), I went through all 255 Z-Wave parameters for one of my 5 Trane TZEMT400AB32MAA's, then again through the promising ones after changing from Run to Hold. Bingo – Parameter 132 it is! Sending a 1 sets the thermostat to Run; sending a 0 sets it to Hold.

    The event below instantly sets all my thermostats to Run mode. Conversely, sending a 0 to the same parameter sets them all to Hold.

    Click image for larger version

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    The old hack involved sending a 255 to the Temperature child device to set Run/Hold (whichever was last set locally at the thermostat), and a 0 for ESM. Bonus tip: Instead of using this hack, set ESM by sending a 2 to Parameter 25. This avoids the hack's side effect of having a 0 temperature reading until the temperature next changes.

    Given how many past treads there have been on this, thought I'd share this solution.

  • #2
    Just tried this on my 2 XR524's. They both report 'ERROR' when trying to read parameter 132. I didn't try setting a value. It may be that different thermostat models support different parameter sets.

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    • #3
      The parameter mapping seems to be unique to each thermostat model.

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