Thermostat fan setting on AUTO but blower runs continuously
Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
Possible Causes
How to Fix / Troubleshooting
Safety first: Turn off power to the furnace/air handler at the breaker before inspecting wiring.
Steps to diagnose:
- Verify thermostat setting: Confirm the Sensi fan mode is set to AUTO, not ON or CIRCULATE.
- Inspect G wiring at thermostat: Remove the thermostat and ensure the G wire is only connected to the G terminal and not touching R or other terminals.
- Check furnace board: With power off, inspect the control board for any jumpers between R and G that may have been installed for continuous fan operation.
- Test without G wire: Temporarily disconnect the G wire at the thermostat, restore power, and see if the fan stops. If it continues to run, the issue is at the furnace board, not the thermostat.
When to call a pro: A stuck fan relay or control board fault in the furnace requires HVAC technician service. The Sensi thermostat is usually not at fault if the fan runs with G disconnected.