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Furnace would not start up...what I discovered

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  • Furnace would not start up...what I discovered

    Just writing this in case someone searches with this specific problem.

    Furnace would not turn on, despite the thermostat being on Heat mode and the set point being higher than the room temp. Furnace (high efficiency) a single stead-on LED on the control board, tied "rebooting" it, nothing. I fixed this furnace a couple months ago, replacing the draft inducer, and started wondering if I did something to ruin it.

    Turned out that the thermostat batteries were low! Even though the thermostat has a low battery icon, it didn't illuminate, and behaved exactly as if it had fresh batteries. On a whim, I replaced them and the furnace started right up.

    I'm making a note to replace the batteries when we replace the smoke detector and CO detector batteries. Hope this help someone with this scenario.

  • #2
    I keep telling myself I am going to put together a long list of things to maintain around my house each year. In my old house I ruined my AC unit by not switching the filter. Kept trying to figure out why it would ice up 1" thick. Felt so stupid ;-) live and learn.


    • #3
      I'm embarrassed to admit that same exact issue cost me $75 in a service call last fall. A little more actually when you figure in the cost of the battery that I sheepishly handed over to the Service Tech. It's already noted on the calendar to change the thermostat battery on Labor Day!
      I decided to change calling the bathroom the "John" and renamed it the "Jim". I feel so much better saying I went to the Jim this morning.


      • #4
        this problem is generally removed when the (C) common terminal is wired to the thermostat and furnace.

        thermostats wear like anything else. as the relays age they require more power to pull down. in a thermostat, it's not a huge amount of power but at some point the amount of amps needed to pull down the relay is more than what the battery has. BUT, the battery voltage is more than the trigger set in the thermostat programming.

        It's very similar to having 12 volts at your car battery, but not able to start the engine. The volts are there, the amps are not.

        ... it was plumbed by Ray Charles and his helper Stevie Wonder