7 Reasons Your Furnace is Blowing Cold Air & Ways to Fix (2023)

If your furnace is blowing cold air in your home, this is a sign of an issue with the flame detector, gas supply, air filter, pilot light, or condensate lines. Many of these issues are able to be easily solved on your own by sanitizing or replacing components in the gas furnace. Let’s discuss the various ways you may be able to resolve these issues on your own.

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Reasons Your Furnace Is Not Producing Warm Air

The Pilot Light is Damaged

If your furnace is blowing cold air, it may be a good idea to check the pilot light on your gas system to ensure it is working. The pilot light in your gas furnace is designed to ignite the burners to ensure your system is able to develop heat. It is common to have issues with the pilot light on older gas furnaces. We recommend following the instruction kit that came with your furnace to re-light the pilot.

Find the Pilot Light Assembly & Reset Toggle

If you’re looking to re-light the pilot light on your own, the first thing that needs to be accomplished is locating the pilot assembly and its reset toggle. The reset toggle is usually located near the bottom of the furnace. Please refer to your instruction kit if you are having issues finding the pilot light assembly and reset switch. After the reset toggle has been located, move it to the off position to deactivate the gas.

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Set the Reset Switch to the On Setting

We recommend waiting a couple of minutes before setting the reset switch to the On position to allow excess gas to exit from the chamber in your furnace. Next, adjust the reset toggle to the Pilot setting to ensure gas is able to be transmitted to the pilot light. After you have changed this setting, locate the reset button on your furnace and hold it down while placing a match in front of the pilot light. You will observe the formation of a flame from the pilot light. Once you are able to start a flame, you will need to release the reset button. Congratulations! You have successfully re-light the pilot light and your furnace should activate to heat your home. If you need assistance re-lighting your pilot light, give our team a call by phone at (703) 543-9649 to receive assistance.

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7 Reasons Your Furnace is Blowing Cold Air & Ways to Fix (1)Dirt & Grime on the Flame Detector

Other types of gas furnaces to not rely on a pilot light to activate the heating process. Furnaces without pilot lights rely on flame detectors to ensure the successful completion of a heating cycle. If your flame detector is covered in dust, dirt, or grime, you will quickly loose heat and your furnace will start blowing cold air. This issue is able to be fixed by simply cleaning the flame sensor in your furnace. Or you may rely on our team of HVAC experts to sanitize the flame detector and restore the heating process.

Air Filter is Restricting Airflow

If the air filter in your furnace is covered in dust, grime, or soot, this will block incoming air from your gas furnace. Common signs of dirty air filters include long heating cycles and overheating issues. The average overheating issue will cause your heater to blow cold air throughout your home. To restore the flow of warm air in your house, we recommend replacing the contaminated air filter with a new one. Since the new air filter will not block airflow to your gas furnace, the unit will no longer overheat.

(Video) Furnace Blowing Cold Air | DIY Common Fixes

A Low Supply of Gas in the Home

If your heater is blowing cold air, this may indicate a severe issue with the gas supply line in your home.Your furnace is designed to deactivate if it’s not receiving enough gas to perform its standard heating process. Unfortunately, there is no easy way to fix this issue on your own. We recommend calling a professional HVAC technician to perform a gas furnace repair project.

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7 Reasons Your Furnace is Blowing Cold Air & Ways to Fix (2)The Condensate Lines are Clogged

Have you noticed your furnace is not working in your home?The latest state-of-the-art furnaces are engineered with condensate drain lines that aid with the removal of moisture. Ifthere is a blockage in the condensate lines, this maydeactivate the burners and cause the furnace to blow cold air in your home.

There’s Damage to Your Ductwork

The furnace may be blowing cold air due to holes and cracks in the ductwork of your home. These small to large openings allow cold air from your attic to enter the air ducts.Your furnace could be blowing warm air and working properly, but could be leaking out by the time it blows out of your vents. Duct sealing could allow the warm air to reach the vents much more efficiently.

(Video) EASY: Furnace or Heater Is Blowing Cold Air - Step by Step Diagnosis and Repair

The Thermostat is Set to On Instead of Auto

If your heater is blowing cold air, we recommend checking the thermostat in your home to confirm its set to Auto. If your thermostat is toggled to the On setting, this will cause your furnace to continuously run throughout the day, even when it is not producing heat. Simply switch this thermostat setting to the Auto channel to ensure the gas furnace in your home will only run during the standard heating process.

7 Reasons Your Furnace is Blowing Cold Air & Ways to Fix (3)Reliable Furnace Repair & Installation Services

If the furnace in your home is blowing cold air, give us a call by phone at (703) 543-9649 or fill out our Service Request Form to receive assistance. Our team of technicians offer comprehensive HVAC repair services in Reston, VA and other areas.

Are you having issues with your furnace? Our professionals provide dependable furnace repair and installation services in your local area. We also offer other HVAC services such as air conditioning repair or replacement. Call us and we will check your furnace and ducts so you will have warm air heating your home for the rest of winter.


How do you fix a furnace that blows cold air? ›

When a furnace blows cold air, there may be an issue with the unit's electronic control panel. This is sometimes easily solved by resetting the system. Turn off power to the furnace at its ON/OFF switch. Wait a few minutes, then flip the switch to ON.

Why is my furnace on but blowing cold air? ›

If you have a dirty or clogged furnace filter, the cool air from inside your home will struggle to travel past through it and into the furnace. This means you have insufficient air to heat and redistribute. The result is your heater blowing cold air.

What causes a furnace not to heat? ›

Dirty filters are the most common cause of furnace problems. Dust and dirt restrict airflow—and if the filter gets too clogged, the heat exchanger will overheat and shut off too quickly, and your house won't warm up. If the blower is running but no heat is coming out, replace the filter.

Is there a way to reset a furnace? ›

Locate the furnace power switch near the furnace and turn it off. If there's no switch, turn off the main circuit breaker to the furnace. Wait for about 10 seconds. Turn the switch or breaker back on and check to see if the furnace is running properly.

What is the most common problem with furnaces? ›

The most common problems with furnaces are: Dirty ductwork. Old filters. Faulty starting mechanism.

Why is my thermostat on but no heat? ›

A clogged filter is probably the most common reason for this problem, so it's a good place to start investigating. Take a look at your filter and, if it's really dirty and clogged, it means there's restricted airflow to your furnace. This may be keeping it from being able to create heat.

What to do when heat is not working? ›

Heater Not Working? 7 Troubleshooting Tips:
  1. Check that your thermostat is set to “heat.” ...
  2. Change the filter. ...
  3. Make sure the gas is on. ...
  4. Clear the chimney exhaust flue. ...
  5. Clean away leaves and debris from exhaust vents. ...
  6. Flush out the drain lines. ...
  7. Check for blocked ducts restricting airflow.
Nov 16, 2016

Where is furnace reset button? ›

All furnaces are equipped with a reset button. They are generally red or yellow and are located inside the blower compartment. The reset button is a safety feature that will shut down the furnace when a problem is detected, often a hot or overheating furnace, before it trips the circuit breaker.

How do you know if your furnace is clogged up? ›

Warning Signs of a Clogged Air Filter
  1. Increased Energy Consumption. When home air filters are clogged, furnaces have to work harder to meet the desired temperature of the thermostat. ...
  2. Higher Electric Bills. ...
  3. Uneven or Poor Heating. ...
  4. Short On/Off Cycles. ...
  5. Indoor Air Pollution. ...
  6. Dust. ...
  7. Burning Smells. ...
  8. Getting Sick.
Jan 11, 2022

Where can I find the furnace reset button? ›

This reset button needs to be pushed in to restart the furnace. The reset button is usually situated inside the blower housing, next to the blower motor. The button may be in red or yellow and easily visible.

How much does a new furnace cost 2022? ›

A new furnace replacement can cost between $3,000 - $7,600, depending on the size of your home, the efficiency of your new furnace, and the sophistication of the equipment. That includes labor and permit fees, not just equipment costs.

What are most expensive furnace repairs? ›

The three most expensive parts on a furnace are the blower motor, the circuit board and the draft inducer motor.

What is the typical lifespan of a furnace? ›


A well-maintained furnace can last at least 15 to 20 years, but completing annual maintenance and being diligent with repairs can extend its life even longer.

How do I know if my thermostat is blown? ›

7 Ways to Tell Your Thermostat Is Broken
  1. Thermostat Has No Power. ...
  2. AC or Furnace Won't Turn On. ...
  3. Heater or AC Won't Turn Off. ...
  4. Thermostat Doesn't Match Room Temperature. ...
  5. Thermostat Doesn't Respond. ...
  6. Short Cycling. ...
  7. Thermostat Forgets Programmed Settings.

What are the signs of a thermostat not working? ›

High temperature readings

The main symptoms of a failing thermostat are related to engine overheating. It can be easily noticed because the temperature gauge in the vehicle will probably read unusually high. This can be caused by the valves being stuck in a closed position.

How do I know if my thermostat fuse is blown? ›

A blown fuse inside your thermostat will cause the device to malfunction. You'll need to open the panel and locate the fuse. This is a small, clear cylinder with metal ends and a filament running through the center. If this filament brakes, the fuse has blown and will need replacing.

Why is my heat not working but cold air is? ›

The Furnace Filter is Dirty

Air filters catch dust and debris we generate in our homes—that means they need to be changed on a regular basis. An overly clogged air filter will limit airflow to your furnace and could cause it to overheat and turn off. Then the furnace blowing cold air is all you're going to get!

Why is my AC blowing cold air when heat is on? ›

When your heat pump goes into defrost mode, it switches into cooling mode, causing the outdoor coils to heat up to melt any frost or ice within the system. However, because the system is in cooling mode, it means that for a few minutes, it will blow cold air through the vents.

What are signs that your furnace is going out? ›

Poor temperature control.
  • Increasing illness symptoms. ...
  • High furnace age. ...
  • High heating bills without explanation. ...
  • Strange noises. ...
  • Pilot flame color changes. ...
  • Dry air. ...
  • Soot. ...
  • Poor temperature control.

Why won't my heat get warm? ›

Low coolant: Whether caused by a leak or water evaporation, low coolant is the most common source of poor heater output. Thermostat: A stuck-open thermostat prevents the engine (and coolant) from heating up. Heater core: A clogged heater core restricts coolant flow, giving up little or no heat.

What to check if heat is not working? ›

Heater Not Working? 7 Troubleshooting Tips:
  1. Check that your thermostat is set to “heat.” ...
  2. Change the filter. ...
  3. Make sure the gas is on. ...
  4. Clear the chimney exhaust flue. ...
  5. Clean away leaves and debris from exhaust vents. ...
  6. Flush out the drain lines. ...
  7. Check for blocked ducts restricting airflow.
Nov 16, 2016


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