Symptoms
- Furnace runs but house stays cool
- Thermostat shows a different mode or temperature than expected
- Worked fine before switching to a smart thermostat
Likely causes
- CommonEco or energy-saving mode activeThese modes intentionally hold a lower temperature to save energy and can be mistaken for a malfunction.
- CommonWiring incompatibility with the HVAC systemSome smart thermostats need specific configuration for heat pumps, multi-stage furnaces, or dual-fuel systems.
- PossibleIncorrect equipment type set in the appChoosing the wrong system type during setup can prevent proper heating calls.
- PossibleSensor placement issue if using room sensorsA sensor in a cold room can pull the average temperature down.
- PossibleUnderlying furnace problem unrelated to the thermostatThe thermostat may be calling for heat correctly while the furnace itself underperforms.
What to do
- Check whether Eco or a similar energy-saving mode is active and turn it off if you want standard comfort settings.
- Confirm the equipment type selected in the thermostat's setup matches your actual system (standard furnace, heat pump, dual-fuel, etc.).
- If using remote sensors, check which rooms are included and remove ones located somewhere unusually cold.
- Verify the wiring against the manufacturer's compatibility guide for your specific system type.
- Feel the supply vents directly; if air isn't warm at all, the furnace itself may not be heating properly rather than a thermostat issue.
- Reset the thermostat's equipment configuration and re-run the setup wizard if a mismatch is suspected.
Tools and parts
- Smartphone with the thermostat app
- Screwdriver
When to call a pro
Call an HVAC technician if the wiring configuration matches your system and vents still aren't blowing warm air, since the furnace itself may need service.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.