14 Reasons Why Your Furnace Is Blowing Cold Air

A furnace that starts blowing cold air instead of hot air is a key indicator that something has gone wrong. Keep reading to find out what might be causing this problem.

Why Is My Furnace Blowing Cold Air?

Listed below are the top 14 causes of a furnace blowing cold air.

1. Broken Thermostat: The thermostat is the control center of your entire HVAC system. When the control center breaks down, the furnace doesn’t know to produce warm air. You can resolve this issue by installing a new thermostat.
   
   
2. The Furnace Hasn’t Warmed Up: Your furnace won’t start circulating warm air the second you turn on the thermostat’s heat setting, especially during the first use of the season. Be patient, and give it some time to work its magic.
3. The Pilot Light Is Out: The pilot light ignites the gas that fuels furnace operation. When this component stops burning, the combustion process halts. All you have to do is relight the pilot light to restore function. In most cases, this will simply be a button.
4. Dirty Air Filter: A dirty air filter can cause the furnace to overheat due to excess pressure. When the furnace overheats, the limit switch shuts down the system and stops heat production. Replace the air filter to prevent overheating.
   
   
5. Malfunctioning Computerized Controls: Modern furnaces are equipped with advanced, computerized controls that alert you when a problem occurs. When these controls malfunction, you have no way of knowing something has gone wrong. Try resetting the furnace to restore heat production.
6. Clogged Condensate Line: Some furnaces have a condensate line that moves water away from the unit. When this line becomes clogged with debris, the furnace can’t ignite. When the furnace can’t ignite, it will only produce cool air. Contact an HVAC technician for assistance in this instance.
7. Overheating System: Furnaces are equipped with a safety component called a limit switch. When the furnace overheats or is at risk of overheating, the limit switch halts operation. This results in only cool air production. Common causes for furnace overheating include worn-down components and a dirty filter.
8. Compromised Flame Sensor: The flame sensor detects the flame inside your furnace. If no flame is present, the flame sensor signals the furnace to shut down. A compromised flame sensor causes the blower to continue running but without a flame for heat production.
9. Gas Supply Issue: Furnaces automatically shut down when they detect a problem with the gas supply. Since gas issues can cause harm, we recommend letting a professional handle any gas supply issues.
10. Cracked Air Ducts: Cracks in the ductwork allow warm air to leak through before it can heat your home. You’ll need to seal the cracks to restore proper airflow.
    
    
11. Restricted Airflow: Airflow obstructions in the ductwork, vents, or furnace itself impede heat circulation.
12. Standing Water Around the Unit: Excess condensation, which is often caused by a clogged condensate line, allows standing water to form around the unit. Moisture in the furnace prevents the system from lighting and, thus, produces warm air.
13. Valve Issue: A faulty gas valve can prevent the pilot light from igniting. When the pilot light doesn’t ignite, it can’t heat the gas coming in.
14. Empty Oil Tank: Just as a gas furnace can run out of its gas supply, an oil furnace can run out of its oil supply. When this happens, the pilot light has no fuel source to heat, and the furnace only produces cool air.

Call Maitz Home Services for All Your Furnace Repair Needs

Is your furnace constantly blowing cold air? The licensed HVAC technicians at Maitz Home Services will help you make things right. No matter when a furnace issue pops up, we have you covered with reliable 24/7 emergency service. Schedule a repair today to restore home comfort.