Q: The fan to my furnace/AC system stays on after the furnace has finished its heating cycle. This causes it to blow unheated air non-stop, using up a lot of electricity unnecessarily. How do I fix it?
A: A faulty thermostat might be the problem. While the fan is stuck running after the furnace has shut off, remove the face of the thermostat, which disconnects the terminals. If this stops the fan, then replace the thermostat. If the fan is still running then the problem might be a problem with wiring, or possibly a faulty control board or Fan & Limit Controller (in older furnaces), which should be set to switch off the fan at a preset temperature. Over time the Controller switches can get rusted and worn out and require replacement.