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When the weather gets cold outside in Northbrook, Illinois, it’s always pleasant to relax indoors with the heat flowing through the rooms. But if your furnace is blowing cold air, you and your family won’t be very comfortable. Here are some of the reasons why your furnace might be blowing cold air and what you can do about it. 

Thermostat Issues 

The first thing to check when your heating system isn’t working properly is the thermostat. It’s possible that someone in your home switched it to the off or cool position by mistake. If it’s still set on warm but is pushing cold air through the vents, check the fan setting on the thermostat. Most thermostats have an option to turn the fan on or to auto. If it’s set to the on position, your heating and cooling system will continue to blow air even when the furnace is off. When you switch it to auto, this may fix the issue if the thermostat is to blame.

Worn Out Furnace Components

There are a variety of parts at work when your furnace is on and running. If you were to peek inside of a furnace while it operates, you’d likely see some gas valves, the motor, and other safety switches that prevent gas from spilling into other parts of the unit. There is also a pilot light, which serves as the source of a live flame when it’s first igniting.

Any of these parts can wear out over time and stop working properly, leading to cold air that blows out of the vents. Everything within your furnace serves a purpose, so each part is important to the heating system.Furnace parts don’t last forever, so if your unit is more than about 10 years old, you’ll likely start noticing more problems that require repair. It’s usually best to replace the furnace after 10 to 15 years because parts will wear out more quickly and you’ll have to bring in a repair technician more frequently.


Overheating is another common problem that may cause your heating system to blow cold air. If this is the issue that’s affecting your furnace, you may notice that it blows hot air first, and then it changes to cold. After a short period of time, it might stop blowing any air at all.

If this happens, turn your unit off and call an HVAC technician for a checkup. Continuing to run the furnace poses a safety risk because it could cause a fire. It can also wear out the heat exchanger, which will be expensive to repair or replace. One cause of an overheating furnace is a dirty filter, so once it cools down, swap it out to see if that fixes the problem.

Pilot Light Out 

If your pilot light goes out, your furnace won’t blow hot air through the vents. You can try reigniting it yourself, but if the flame won’t stay lit, you may not have enough gas coming through the system. Contact an experienced technician to take a look at it. Keep in mind that some newer units have electronic pilot lights, so never put a flame into your furnace if that’s the case. 

Engaged Safety Switches

As mentioned, there are some safety switches within your furnace that help protect your home and the unit from overheating. If one of these mechanisms is tripped, the system will shut itself down to prevent an open flame from moving into other parts of the furnace. This is a complex problem that should always be addressed by a licensed HVAC technician. He or she will have to open up your furnace to figure out what caused the system to engage the safety mechanism and fix that problem, then flip the switch to allow it to produce warm air again.

Here in Northbrook, our team at Ireland Heating & Air Conditioning Co. is always available to address HVAC problems. If your heating system is blowing cold air, contact us at 847-388-0108 to find out how we can help.

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