I just got some info that may help. See this google doc https://docs.google.com/spreadsheets/d/1VQ5RKnu5wZUIdHfiWDm2ZcqK4KqLm_2zuZBcYDqasQI/edit?usp=sharing There are some wires that look like they may be touching, I will ensure they are not tomorrow. See the image in the google doc.

My house heater (gas) will turn off after running for some time but before reaching the temperature set at thermostat. I then have to lower the temperature at the thermostat below the current house temperature (I hear a loud click from the return register) and then back up to a level above the current temperature. The cycle then repeats.

For example:

The thermostat reads 68 but is set to heat to 72. The heater is off. I lower the thermostat to 67. I hear a click. I raise the thermostat to 72. The heater turns on.
Some time later the heater turns off, but it does so before reaching the level set at the thermostat. I repeat the cycle.

Last year I had two separate techs come out and they did not find any issue. One adjusted something and the issue seemed to be better for a while but neither fixed the issue.

Any thoughts on this or is there a stack exchange better suited to this question?

The heater is original I believe, installed in 97. It is gas like I said and I change the return register filter regularly.

Thank you

Edit - Thermostat is an emerson up500W. It is set to a single stage gas heater and the reversing valve position is set to "O" (but "B" is an option). The device says the batteries are full. https://ibb.co/pnGbvQR https://ibb.co/k3d8xJz https://ibb.co/bdfXgmL

I apologize but I do not know anything about the furnace. I will crawl up into the attic and take a look tomorrow and get a model number.

  • Can you give us any info on the model? Of the thermostat, or furnace Closed combustion or open combustion , any error lights on the furnace control board. Although this sounds like a thermostat issue to me that would be jumping to cause in this case. Batteries in the thermostat? Programmable? Lots of possibilities here. This would be the correct place for stack exchange.
    – Ed Beal
    Commented Dec 11, 2020 at 23:27
  • Thank you Ed. I have edited my question with some additional details.
    – Dennis_M
    Commented Dec 12, 2020 at 2:16
  • Yes, we'll need make/model info for the furnace to do much more Commented Dec 12, 2020 at 2:56
  • The next time it happens look for the error code inside the furnace. It's going into lockout.... but it's a 'soft' lockout? (Why is it going into lockout.) Usually they need to be power cycled to reset, not just a momentary stop of calling for heat.
    – Mazura
    Commented Dec 12, 2020 at 3:07
  • Would you add some timing details please? How long (minutes) does the furnace run before it shuts itself down? How long after you adjust the thermostat down then up before the furnace runs again? Are the cycles (time to auto shutdown, time to restart after thermostat turned down then up) after that about the same length?
    – wallyk
    Commented Dec 29, 2020 at 8:38

2 Answers 2


What I would try since it is a single stage gas and not sure if it may be a Tri state relay in the thermostat. Pull the thermostat and connect the wires together and let the furnace / home get to temp so let it run for at least a normal time or longer. Then separate the 2 wires and wait at least 20 minutes. Reconnect the wires and if the heater starts properly it is the thermostat, even though the battery indicator states ok try new. The set point may be off because of a span or dead-band setting. I scanned the users manual and did not see a dead-band and this is unusual for a system that can heat and cool. If things work just connecting the wires removing and connecting and the battery doesn't fix it I would look for a master reset there may be a programmed hold that is causing the issue.


I don't think it is a furnace issue at all. If the techs found no issues and didn't replace anything id say to repl3acd the thermostat. Keep in mind most thermostat are designed to kick in at a set temperature, once reached, they will not call for more heat until they drop a programmed or set number of degrees. This is done to prevent constant cyling the moment the room drops a degree after the room comes to temp. Yours may be getting old and its calibration could be off, which is why its not quite reaching your set temperature. Low voltage thermastats are cheap and easy to replace.

  • As far as a calibration issue that may be true but that would not cause a lockout.
    – Ed Beal
    Commented Dec 12, 2020 at 15:05

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