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Programable shuts off on cycle

Stevers923
Stevers923 Member Posts: 2
in Gas Heating

I have a forced air gas furnace. I am currently using a Sensi programable thermostat. Every time the furnace calls for heat, the thermostat goes black and you can hear it click. As soon as the cycle starts, the thermostat will turn back on. This is my second thermostat, the first one was a Honeywell. This leads me to believe it is not a thermostat issue. Any help would appreciated.

Thanks

Comments

  • HVACNUT
    HVACNUT Member Posts: 6,607

    Battery powered or 24 volt powered thermostat? Is anything connected to the C terminal?

  • Jamie Hall
    Jamie Hall Member Posts: 25,668

    Well… except it is a thermostat issue. A thermostat should simply close a circuit to tell whatever it is connected to to run. Nothing more. However… many newer thermostats aren't just switches — they have a variety of power consuming sensors and lights and computers as well.

    Which need to be powered.

    So, as @HVACNUT enquied? What is powering this thermostat? Batteries? C wire?

    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 10,198
    edited February 13

    As above, @HVACNUT & @Jamie Hall are interested in getting more information about your problem. I might add that the model number and brand of your "Gas Warm Air Furnace" might help me/us to find out where your issue might be.

    I guarantee you that this is not the gas furnace you have:

    Screenshot 2025-02-13 at 3.20.02 PM.png
    Screenshot 2025-02-13 at 3.22.02 PM.png

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

  • Stevers923
    Stevers923 Member Posts: 2

    It is a 24 volt system with battery backup. The system is an International Comfort Products, model F9MXE0801716A2. It does has a "C" wire. It also is using "RH", "Y", "G", "W/E" and the "C" wire. It is wired for Air Conditioning as well. We moved into the house about 5 years ago and it was here when we moved in. I saw a Feb 2016 date on the unit. Thanks for your replies so far.

  • HVACNUT
    HVACNUT Member Posts: 6,607

    If the thermostat is 24 volt powered AND has battery backup, I'd lean towards the thermostat. But you tried a Honeywell also and the same thing? Screen went black? The fact the the same thing happened with 2 different thermostats tells me it's wiring or controls.

    You also didn't mention Rc in the thermostat wiring. Is anything on Rc? With a gas fired furnace with AC, it should be one control transformer. So typically you would jump Rc and Rh at the thermostat. It depends on the thermostat. Honeywell has a tab to move for Rh. Nest needs 24 volts on Rc.

  • Bernie_the_Brewer
    Bernie_the_Brewer Member Posts: 12
    edited February 14

    What feeds your 24VAC?

    I had a similar problem. I had an old Honeywell RA832A switching relay, but that does not have a C-wire output. I modified it to bring the other side of the transformer out, and used it to power my new Honeywell WiFi thermostat. The voltage from the RA832A transformer was a little low, but it powered up the thermostat just fine.

    However, when it called for heat, the load from the relay coil caused a transient drop in the output of the transformer, in turn causing the thermostat to shut down/go black/reboot.

    I had to upgrade the transformer. I thought about adding a larger (40 VA) external transformer, but in the end I just upgraded my switching relay to something with an existing C-wire output (Taco SR501)

    Long story short, it could be that your 24 VAC transformer is undersized.

    Trying to keep Bernie burning!

    Stevers923

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