Fan Runs Continuous
- Category: Common GAS FURNACE Heating Issues
- Published: 21 November 2013
FAN RUNS CONTINUOUS – The thermostat maintains the correct temperature, but the indoor fan never quits blowing.
POSSIBLE PROBLEM & DESCRIPTION
Thermostat "Fan" Switch
- The most common cause of this problem is the “Fan” switch on the thermostat. It normally has two options – “Auto” and “On”. In the “Auto” position, the fan should cycle on only when there is a call for heating or cooling. In the “On” position, the fan will run continuously. Watch Video.
- Some new thermostats have an additional fan setting of “Circ”, which is short for “Circulate”. In this mode the fan will cycle on and off with heating & cooling, but it will also kick-on automatically if there is an extended period without a demand for fan – to provide additional air circulation.
- If your system has an added humidifier, this could cause the system to run more than normal.
- Some humidification system energize the blower to operate even when the heating system is not running to maintain the humidity setpoint in the space.
Stuck Blower Relay - Qualified Technician Recommended
- Many gas furnaces have either a fan relay or a control board to cycle the fan on and off as needed. Sometimes the relay or control can stick which will cause the fan to run continuous.
Stuck Fan Switch - Qualified Technician Recommended
- Some older gas furnaces use a heat-activated fan switch to start the blower after the burners have fired and the heat chamber has warmed-up.
- The fan should stop once the burners go off and the heat chamber cools.
- A stuck fan switch can cause the fan to run continuous.
- Some "Fan&Limit" switches have a push-button, manual-override that, when depressed, causes the fan to run continuous.