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  1. #1
    Join Date
    Dec 2007

    trane heat pump - aux gas heat comes on without furnace blower?!

    hello all - i have what i think are two issues with a system installed this spring (trane xl14i heat pump, xv80 variable speed gas furnace and visionpro iaq thermostat with outside temp sensor). it seems that the aux heat will come on without the furnace blower on (i.e. just the gas is on), which causes the side of the furnace to become very hot, and hot air felt at the furnace air intake inside the house. the first time this happened was about 4 days ago at 4:00am. the smoke detectors woke us up. the trane folks came out and could find nothing wrong. the same situation happened tonight (heat and aux heat had worked fine for about a month before this, which makes me think something broke rather than an installation problem). after the system sat for about two hours, i checked the setup:

    0210 external fossil fuel kit set to "thermostat controls backup heat"
    0342 outdoor temp sensor set to "remote sensor"
    0345 set to "balance point only"
    0350 heat pump compressor lockout set to 35 degrees

    thermostat indicated 67 degrees. temperature was set to 67, so i turned the system on and set the temp to 68. heard the outside compressor come on, the blower came on, and "heat on" was displayed. after about a minute "aux heat on" was displayed. i checked and the gas furnace was on *as well as the compressor*. shortly after that 68 degrees was reached and everything turned off.

    questions: in the above configuration the aux heat should never come on above 35 degrees, and the compressor should never come on below 35 degrees... right?

    is there a situation where both main and aux heat would come on at the same time?

    what could cause the furnace to run without the blower? (and why isn't there some sort of interlock?!?!)

    possible problem? the circuit board in the furnace fried?

    the trane people will be out friday afternoon. this is under warranty, so this is just for curiosities sake. thought someone might have an idea.

    Last edited by Atarian; 12-07-2007 at 04:59 AM.

  2. #2
    Join Date
    Dec 2006
    Middle Tennessee


    the only time that the heat pump and furnace should run at the same time is when the heat pump is in defrost!

    why are you locking out the heat pump at 35 degrees?

    are you giving the stat time to control things properly?

    is it doing the same thing when the technician is there?

    have your hvac company check all of those set-up parameters, dont change it yourself you may void your warranty!


  3. #3
    Join Date
    May 2000
    Indianapolis, IN, USA
    Why didn't the furnace bring the blower on itself? Time for a dealer to look at it.

  4. #4
    Join Date
    Dec 2007
    thanks for the replies so far. heat pump lock out set to 35 degrees was the setting in there - i don't know what some of the others do, so i didn't change anything, just wrote down the values. the problem would not show up (of course) when the tech was here a few days ago.

    even though this is a super wham-a-dyne thermostat, we set it to permanent hold at 67 degrees - i can't imagine that should cause a problem(?).

    as i type i'm waiting for the service folks to call back...


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