Find out why and how to fix the problem

If your furnace is blowing cold air when it should be warm, there could be an easy fix, or it could be a sign of something more serious. When your furnace hasn’t run for a while, cold air is normal at first due to the air in the ductwork being cold and needing time to get warm. If the air doesn’t turn warm eventually, several things could be wrong.

Reasons Your Furnace is Blowing Cold Air

Pilot Light is Out or Damaged
Most modern furnaces manufactured since 2010 do not utilize pilot lights; however, if your furnace is older a pilot light could be the issue. The pilot light is used to ignite the burners in your furnace. If the pilot doesn’t light, there could be a faulty gas valve. If it’s still lit and you notice flickering or the base of the flame is yellow instead of blue, there could be a blockage. If your pilot light is out, you can follow the manufacturer’s instructions on how to relight it safely.

A faulty thermocouple (a sensor that controls the gas valve and the ignition) could be the culprit if the pilot light keeps going out. Normally, there is a simple solution, but you would need a technician to fix the problem.

Flame Sensor
Furnaces without pilot lights rely on flame detectors to complete the heating cycle. You will quickly lose heat, and your furnace will start blowing cold air if your flame detector is dirty. We recommend reaching out to a local dealer for assistance.

Dirty Air Filter
Your furnace works harder and the airflow is restricted when there is dirt, dust and other contaminants that the air filter traps to keep the ductwork and furnace clean. This can cause your furnace to overheat and shut off. Regularly clean and replace your air filter (usually every three months but timing may vary based on filter size).

Low Gas Supply
Your furnace is designed to shut off if it’s not getting enough gas to perform the heating process. Check your gas line. If it’s been damaged, your furnace, water heater or gas stove won’t be working.

Clogged Condensate Lines
Some gas furnaces have condensate drain lines to help remove moisture. If there is a blockage to the lines, it could deactivate the burners and cause your furnace to blow cold air. Make sure the PVC pipe that leads to the floor drain is cleared of any blockages.

Ductwork Damage
There could be a leak in your ductwork due to the general wear and tear, causing cold air to enter your home or your conditioned air to not be delivered into your home. Check your duct system for any holes or poorly connected ducts. If you can find the leak, placing tape designed for ductwork may help, otherwise, call an HVAC professional to do a thorough inspection of your duct system.

Thermostat Issues
Make sure your thermostat is set to “heat.” Next, check to see if the unit’s fan is set to “on” or “auto.” If it is set to “on,” the furnace will run continuously even when it’s not heating the air. Switching the fan to “auto” will only run when the furnace is heating the air.

Batteries could also cause some issues. Some thermostats don’t need batteries to work and may only have a battery backup; some run solely on batteries. Make sure if your thermostat is one that works on batteries only, that they’re new. Batteries don’t have to be completely dead for the thermostat to malfunction.

Faulty Circuit Control Board
Your furnace’s circuit control board relays instructions to various components. When it receives a command from the thermostat to start the heating process, it sends out signals to turn on the blower and the burner. If the circuit control board is malfunctioning, it could turn on the blower and not the burner. So, if your furnace is blowing cold air, it could be because the circuit control board didn’t turn on the burner to heat the air. Make sure your circuit control board is cleaned during your regular maintenance.

How to Prevent Furnace Blowing Cold Air

With regular furnace maintenance and tune-ups, the issues that lead to your heater blowing cold air can be avoided. During an annual checkup, a certified HVAC professional will inspect, clean and adjust all connections and determine if any parts need to be replaced. Regular maintenance offers several benefits, including improved energy efficiency, extended lifespan and reduced risk of breakdowns. Become proactive to prevent potential issues from occurring. Schedule your annual heating maintenance today with your local Lennox Dealer.