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Why Your Furnace Only Blows Cold Air At Night And How To Fix It

My Furnace Turns On And Off Just About Every Second: Why And How To Fix It?

You may have observed that a furnace, which is a device supposed to keep you and your family warm, really blows frigid air at night. You might be unsure about what to do when this occurs.

Due to problems with one or more of the following compartments, your furnace only blows cold air at night:

  • Thermostat
  • Circuit Management
  • Furnace Burner
  • Flame Detectors

You need to troubleshoot to determine which of these compartments is causing your furnace to only blow chilly air at night. then fix it by sanitizing, repairing/resetting, or changing the component.

Learn more about how a furnace operates, how these compartments operate, and how to troubleshoot your furnace to find and fix this issue by reading on.

How A Furnace Operates

A furnace is a heating system used to keep a home or other building warm. A furnace operates by removing cold air from the outside, heating it, and then letting the hot air into the house.

Only a few essential actions carried out within the furnace’s mechanism enable this activity. These are what they are:

  • The thermostat kicks off the processes by telling the furnace to fire up.
  • The process continues at the burner, where natural gas or propane is ignited.
  • The internal sensors of the furnace must then confirm that each burner has been lit.
  • This heat is transferred to the heat exchanger.
  • It then creates warm air by mixing it with cold air drawn from the environment and transferring it into its chambers.
  • When the air is warm enough, the blower starts to distribute it around a home while pulling cool air from the atmosphere of the building back into the furnace through a network of channels.

Why Only At Night Does My Furnace Blow Cold Air?

Your furnace is spewing chilly air only at night for a number of reasons. Your thermostat, circuit board, furnace burner, or flame sensors can be the source of the issue.


Why Your Furnace Only Blows Cold Air At Night And How To Fix It

One of the crucial control devices in a furnace, a thermostat monitors changes in the ambient temperature to maintain a constant balance in the home’s temperature.

The thermostat tells the blower to turn on when the temperature in a room dips below or exceeds a certain point. Because your thermostat is set to “ON” rather than “AUTO,” your blower continues to blow air even when your furnace is not turned on, which may explain why your furnace is blowing frigid air.

On the other hand, it’s possible that your furnace is spewing chilly air as a result of your thermostat being set to cool. It’s possible that you’ve had the thermostat set to cool since the last hot spell or summer.

Circuit Management

Why Your Furnace Only Blows Cold Air At Night And How To Fix It

A processing unit’s circuit control is quite similar to a furnace’s. It gathers data from the thermostat and transmits the appropriate data to the furnace.

A defective circuit control could turn on a furnace’s blowers but leave the burners off.

Furnace Burner

If your burner is blocked with debris, your furnace can be spewing cold air. This is as a result of the thick materials preventing the burner from lighting. Your furnace may occasionally blow chilly air while other times it blows hot air if the burner becomes occasionally clogged.

Flame Detector

An vital part of a furnace is a flame sensor. The furnace’s ability to operate properly can be hampered by problems with the flame sensor. The furnace might not heat its coils if your flame sensor is not functioning properly.

After some time, the burner turns off as a result of the malfunctioning flame sensors. As a result, the furnace operates for a brief period before ceasing (blows hot air during the day and cold air at night).

How Can I Stop My Furnace At Night From Blowing Cold Air?

Why Your Furnace Only Blows Cold Air At Night And How To Fix It

Furnaces often blow hot and cold due to problems with the flame sensors, however this is not always the case.

The best method to deal with this issue is to troubleshoot any detected issues before offering a solution. Here is how to diagnose your furnace step by step:

Turn On The Furnace’s Power

You must check to see if the furnace is plugged into the electrical supply.

You would have to check the power connection to make sure there is electricity.

Review the circuit breaker box to make sure it hasn’t tripped off and check the circuit control to make sure it’s operating properly. If your furnace is not currently connected to electricity, you should do so. If the circuit breaker has tripped off, repair or replace the defective circuit controls and turn it back on.


The thermostat should then be checked to ensure that it is set appropriately for your needs. You should have your thermostat set to your favorite temperature and the warm setting.

Additionally, confirm that your thermostat is on AUTO rather than ON or OFF.

If the thermostat seems to be causing other issues, you should try to fix or replace it.

Furnace Blower

If your thermostat turns on, you should check to verify if your furnace blower operates. Remove the furnace blower for additional inspection if it is not operating. A professional’s services would be required if it seemed damaged.

Air Filter

Check the air filter to make sure it is operating properly. To thoroughly inspect the air filter, you might need to remove it. For the furnace to perform properly, an air filter needs to be maintained by being cleaned sometimes and replaced every three months.

How Can My Furnace Be Reset?

Because most furnaces now have a connected reset button, it is much simpler to reset one. However, there is a little more to resetting a furnace than simply pressing the reset button. Here’s how to reset your furnace step by step:

  1. Make sure the pilot light is turned off.
  2. Turn off the central gas supply path to your furnace while maintaining the pilot gas supply on.
  3. As low as possible, lower the thermostat’s temperature setting.
  4. To stop the electric supply to the furnace, shut off the circuit breaker in its box.
  5. To rekindle the pilot light, light a match and hold it until the pilot flame jet opens.
  6. Reset the circuit breaker, then reattach the primary gas supply.
  7. Reset the device by pressing and holding the button in the blower part for at least 40 seconds. Then, adjust the thermostat to the appropriate setting.

Why Is My Furnace Taking So Long To Warm Up?

Problems with your thermostat or flame sensors are the reason of your furnace’s inability to reach temperature.


Your furnace’s thermostat regulates the temperature levels, keeping them balanced. Your thermostat can be dusty, broken, or not in the right place if your furnace is having trouble heating up.

If your thermostat is unclean, you should gently clean it as its sensitivity makes it vulnerable to injury. Where it has been harmed, a new one needs to be installed.

Last but not least, if your furnace has a mechanical thermostat, make sure you place it correctly and away from a wall. This will ensure that it accurately reads the room’s temperature.

Furnace Sensors

Your flame sensors may be clogged or defective if your furnace is having trouble heating up. If it is dirty, you might need to properly clean it. It is better to replace it if it has damage and is dysfunctional.

Where Can I Find The Furnace Sensor?

Knowing where a furnace sensor is positioned is crucial. This knowledge is essential for safety and troubleshooting. Your furnace’s sensor is a thin, bent piece of metal that is attached to the burner assembly in front of the pilot frame.

How Can I Clean The Flame Sensor In My Furnace?

The following is a step-by-step guide for cleaning a furnace flame sensor:

  1. Disconnect the gas and electrical supplies to your furnace.
  2. Remove the flame sensor from the burner assembly that is located before the pilot frame.
  3. Clear the flame sensors of any debris.
  4. Sandpaper or other abrasives could be used for this.
  5. Reposition the flame sensor, then turn the furnace back on.


A furnace may not reach the desired temperature or may blast chilly air at night for a variety of reasons. While there may be a number of reasons, the thermostat and the flame sensors are the two most common.

Why Your Furnace Only Blows Cold Air At Night And How To Fix It

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Written by HVAC Contributor

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