I have a regular gas air heater that heats the whole house. It is installed in a garage.

When I use thermostat to turn on the heat it works as expected. When temperature reaches set value the gas turns off.

But the fan keeps running, cycling room temp air around. It never turns off. I waited at least an hour.

I replaced a thermostat. Same problem.

1 Answer 1


There should be a switch on the thermostat that says "ON AUTO", make sure it's set to AUTO.

If the switch is set to auto, but the fan continues to run. You may have a short between the R wire and the G wire, or a problem with the control board in the furnace.

  • It is set to auto of course. I rewired it when I was switching thermostats. I think I need to look at the board. The issue is intermittent. Happens about half of the times.
    – Zepplock
    Commented Dec 27, 2014 at 17:52
  • If it's not all the time, it could be a bad limit switch.
    – Tester101
    Commented Dec 27, 2014 at 18:22
  • Is that on a board or a separate switch? I have a small box with in/off switch that turns the whole furnace off.
    – Zepplock
    Commented Dec 27, 2014 at 19:27
  • The limit switch is a sensor in the furnace that opens if the furnace gets too hot. In most furnaces, if the limit opens, the blower stays on to remove excess heat.
    – Tester101
    Commented Dec 27, 2014 at 21:06

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