I have an older furnace with a Honeywell fan limit switch. The unit ignites, heats up and then the fan comes on normally. When it gets to the proper temperature the heating unit shuts down and the fan continues to run, as it should, as the unit cools down. The problem is that the fan doesn't shut down and the heating unit fires up again regardless of if it's at the proper room temperature or not. This seems to cause a continuous heating cycle and really eats up the natural gas bill.
Any ideas are appreciated


Mike

Could be a fan and limit control they do go out of calibration. Also it could be the thermostat heat anticipator setting.

The fan limit control switch controls the temp of the on and off the blower with a limit if the blower doesn't come on it kills 24v or 115v to the unit to shut it down. But a stuck or weak combination switch will not make it call for heat. Is it heating your house above the set temp, or is it just running a lot? If you have a lot of air leaks around the windows and doors you will get the same symptom.