Hello I just replaced my old White-Rodgers thermostat because it just wasn't working consistently (sometimes it would turn on the furnace, but mostly it wouldn't). I swapped it with a White-Rodgers Sensi thermostat.

Once I replaced the thermostat, the furnace turned immediately upon adjusting the thermostat to do so. (I'm thinking job well done right now)

Once the home reached it's target temperature, I felt cold air blowing. The furnace no longer blows hot air. Something happened while the furnace was running or about the time it got to it's stated temp that it just quite blowing hot air. Now it will not blow warm at all. Any ideas where to start? I'm going to replace the filter today and see if the Pilot is still lit, but I've not gone up in the attic yet.

The furnace is one without a pilot, it has an auto-ignition if that matters.

  • 1
    What is the make and model of the furnace? Does the furnace continually blow air (cold or hot), or does it turn on and off? If the blower is blowing constantly, you likely have a bad/open limit switch. You should test the continuity of each limit, to determine which one is open. If none of what I just said makes sense to you, contact a local HVAC company. – Tester101 Mar 2 '15 at 18:44
  • Thank you for the comment, it's a carrier furnace model gb3aav. Also I re-attached the "old" thermostat to ensure that the issue isn't the t-stat. Now the heater works again (kinda). The reason I replaced the old t-stat, was that it would call for heat, and the furnace would start up, then randomly shut off. The length of time the furnace would stay on is pretty random (1 to 5 secs). If it stayed on beyond 5 seconds, then I was likely going to get heat (though even today, the heat just shut off after about 5 minutes mid-cycle) before it reached it's target temp. – Belacyrf Mar 3 '15 at 19:29

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