If you smell gas, leave the area and contact the gas utility or emergency services. Do not keep troubleshooting a possible gas issue.
Check the thermostat first.
If the fan is set to On, the blower can move air even when the furnace is not heating. Set the fan to Auto and make sure the thermostat is calling for Heat.
Check the filter.
A dirty filter can restrict airflow and cause the furnace to overheat. Some furnaces shut the burners off for safety while the fan keeps running, which feels like cold air from the vents.
Watch for short cycling.
If the furnace starts, stops, and starts again repeatedly, it may have airflow, ignition, sensor, venting, or control problems. That is a good time to request service.
Do not bypass safety parts.
Do not tape switches, bypass sensors, or keep resetting a system that shuts itself down. Those safeties exist for a reason.
When to request help
- Furnace never produces warm air
- System shuts off repeatedly
- You smell gas or burning
- Breaker trips
- Filter change does not improve airflow