Furnace has one job: distribute warm air through your home, so that you and anyone else who lives there can be comfortable when it is cold outside. If a furnace is not producing heat, it is often a cause for alarm, but in many instances, it might not be that big of an issue. One of the reasons your furnace might be blowing air but not producing heat is if there is a fan setting on your thermostat.
The Furnace Keeps Turning on and Off
As a furnace heats your home, it typically cycles on and off. It tries to maintain the temperature set on the thermostat. Depending on the programmed temperature and the outdoor temperature, a furnace might cycle on, heat the room or home to the desired temperature, then cycle off again several times an hour.
If a furnace starts short cycling or turning on and off frequently, without ever reaching the set temperature, that is usually a sign that something is wrong. During a short cycle, the furnace will only run for some minutes before it turns off again. Often, the cause of a short cycle is a lack of airflow in the furnace, that causes it to overheat. Furnaces have safety switches built-in that will shut down the system if the temperature gets too hot.