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Auxiliary Heat for Trane XL15i with Ecobee3 - not heating when temperatures go below 20

hidlynhidlyn Southern MarylandMember
edited January 6 in ecobee

We have a Trane XL15i unit in our attic that takes care of the upstairs with a dual zone set up (both zones have an Ecobee3 - one in the upstairs hallways, one in the master bedroom) and a Trane XL16i in our basement which takes care of the 1st floor and basement.

Last year, I installed an Ecobee3 in our family room for the Trane XL16i. We had good luck with it, so when some repairs needed to be done on the dual zone in the attic, I had the tech install 2 more Ecobee3 in the upstairs hallway and master bedroom. We had no troubles that winter, I believe now, because it was so mild, rarely dropping below 20.

This year, with the sudden downturn in temperature to -2 with windchill, the attic unit (1 stage heat pump/1 stage aux with C wire) has been unable to maintain the heat. The hallway is part of a second story foyer so stays warmer from the downstairs temperatures (between 67-69F). However, our bedroom (with the door shut) is as low as 58F during the nights when set to 65-68F.

Two techs have been out now. The first said he found some wire loose and fixed it. Did not help. The lead tech came out and found holes in the duct hoses, 6" big for the one. He fixed those and some deteriorating tape. He reset some settings on the Ecobee to what he likes - Enabled Comp/Aux on together, and disabled the compressor minimum outdoor temperature saying it would not hurt our unit to keep running, just less efficient. After he left, we still had an issue where the bedroom was 59F in the middle of the night.

After researching the web, I see some people who had similar issues found out that the auxiliary was never working when called for despite it looking like auxiliary is on. One mentioned a faulty wiring and another a burned out wire. In order to test if this is our issue with the upstairs unit, I turned the Max. Aux. Temp. to 20 (it's 19 outside today) and put the system into Aux only on both Ecobee3 thermostats. After several minutes, there was no air and no heat coming out of the vents. I tested the downstairs unit as well (a 2 stage/1 stage aux). In Aux only mode, it was blowing out very warm air with just a bit less air force than the heat pump.

My question is whether this type of test would tell a tech to look for issues with the auxiliary wiring upstairs on the attic unit. After having them here twice, I am hoping they figure it out this next time. I am fairly convinced we have an issue with the wiring for the auxiliary heat (which is electric).

TIA for any help or suggestions.



  • kevinmcckevinmcc Macomb, ILMember

    Max. Aux. Temp. is if the temp is higher than 0 F, AUX will not run if temp is 19. I normally have this at 35 F so if heat pump is not working AUX will run and heat house and no worries of frozen pipes.

    What do you have for a zone controller?

    Is your zone damper to the bedroom shut or stuck partially open?

    Do you have stage thresholds set? I would set Heat Differential Temp to 1 degree and Heat Differential Temp 3 degrees.

    Do you have smart home and away enable? I would disable.

  • hidlynhidlyn Southern MarylandMember

    I wrote that incorrectly. The Max. Aux. Temp. is set at 20F. I will edit that. I can set it higher though and try again. Thank you.

    Do you ever have the comp/aux working together enabled? The last tech set it to that.

    The damper is fine I was told. The thermostat is the only thing I know of that controls the operation of the damper. They checked it out yesterday. We are getting air flow now because with the warmer temps today the heat pump kicked in. I do not have smart home and away enabled. No need for them.

  • kevinmcckevinmcc Macomb, ILMember

    Yes, do use the comp/aux if your system supports that.

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