How To Fix A Furnace Blowing Cold Air

A furnace blowing cold air can be a frustrating and uncomfortable issue, especially during the colder months. If you’re experiencing this problem, there are a few potential causes and solutions to consider. This guide from our HVAC professionals at Oliver will help you troubleshoot and understand how to fix a furnace that is blowing cold air.

Step-by-Step Instructions:

1. Check The Thermostat Settings

Before inspecting the furnace itself, ensure that your thermostat is set correctly. It should be in “heat” mode and set to a temperature higher than the current room temperature. If your thermostat runs on batteries, replace them and check if that resolves the issue.

2. Inspect The Air Filter

A clogged air filter can restrict airflow and cause the furnace to overheat, triggering a safety shutoff. Locate the filter, typically found near the blower compartment or air intake, and check if it’s dirty. Replace it with a clean one if needed.

3. Verify The Pilot Light Or Ignition System

For older furnaces with a pilot light, check if it’s lit. If not, follow the manufacturer’s instructions to relight it. If your furnace has an electronic ignition system, inspect it for visible damage or debris and clean it with a soft brush.

4. Reset The Furnace

Many modern furnaces have a reset button, typically located near the blower motor. Press the button once and wait a few minutes to see if the furnace starts producing warm air again.

5. Check The Gas Supply

Ensure that the gas valve supplying your furnace is open. If you suspect a gas leak (noticeable by a rotten egg smell), turn off the gas supply immediately and call a professional at Oliver.

6. Inspect The Flame Sensor

A dirty or faulty flame sensor can prevent the burners from staying lit, leading to cold air being blown through the vents. Turn off the power to the furnace, locate the flame sensor near the burners, and clean it with a soft brush or fine sandpaper.

7. Examine The Ductwork

Leaks or blockages in your ductwork can result in cold air coming from your vents. Inspect visible ducts for gaps, holes, or disconnections and seal them with duct tape if necessary.

8. Check For Error Codes

Most modern furnaces have an LED indicator that flashes codes to signal issues. Refer to your furnace’s manual to interpret any displayed error codes and take appropriate action.

9. Test The Blower Motor

If the furnace is running but only blowing cold air, the blower motor may not be functioning properly. Use a multimeter to check for electrical continuity. If the motor isn’t working, it may need to be replaced.