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Why Is Your Furnace Blowing Cold Air?

A furnace blowing cold air in your Riverside home could be a big problem. When a furnace isn’t producing hot air, it has one of a handful of common issues that an HVAC technician can quickly address.


It could be your thermostat that is generating the problem. If so, the solution could be as simple as flipping a switch.

Suppose the thermostat is switched to “on,” and your furnace occasionally blows cold air. The reason is that your furnace is not producing heat nonstop.

The burners are activated and send warm air through your ductwork when the thermostat indicates that the temperature in your home is lower than your desired temperature setting. Once the temperature hits the desired setting, your furnace turns off until the temperature drops again.

If the fan is set to “on” constantly, it will blow air even when your furnace is resting. It’s better to set the fan to “auto.” This way, the fan will only blow when the furnace produces hot air.

Another easy-to-fix problem is that your battery-powered thermostat has a low battery. It is easy to forget to check the battery because thermostat batteries can last for years. Check the batteries before contacting an HVAC professional if your furnace is pushing out cold air.

There are thermostat issues where it is best to reach out to the technicians at Dragonfly Heating & Cooling for help. For example, you may have installed a home thermostat incompatible with your HVAC system. Or a do-it-yourself thermostat installation may not have turned out as well as hoped. In these cases, don’t worry. Our professional technicians will be able to sort out the issue, identify its cause, and provide clear solutions.


The condensate lines of your HVAC system require regular maintenance. They are part of what our HVAC technicians at Dragonfly Heating & Cooling check during our annual inspection of your unit. If your HVAC system is functioning during hot weather, the condensate unit is constantly dripping water into the pan. Over the summer, your condensate lines can get plugged with dirt and grime. When they get clogged, the water level rises, the float switch is tripped and your HVAC system shuts down.

Grime buildup tends to peak towards the end of the warm weather, right before you want to use your furnace. Consequently, since the float switch is tripped, it starts blowing cold air when you turn your furnace on. Prevent this by scheduling regular annual maintenance for your HVAC unit.


Your pilot light ensures that there is constantly a flame source to ignite the burners in the furnace. This allows heat to be created within the furnace and distributed throughout the home.

A pilot light can get blown out or go out on its own. All it takes, especially on older units, is a stiff breeze or someone walking quickly by the furnace at the right moment to cause this. If the gas company was performing maintenance on the lines, they might have caused your pilot light to go out.

Your furnace might need to be cleaned. If the small orifice that fuels the pilot light is dirty, it can impact how it burns. If you notice that your pilot light is constantly going out, it could be that it is not getting enough fuel to sustain itself.

If your pilot light is burning yellow or red, this is an indication that it is not getting enough fuel. An adequately fueled pilot light will burn bright blue. To keep your furnace working at peak efficiency and ensure that all parts are clean and in working order, you should have professional maintenance and duct cleaning scheduled at least once a year.


If your burners cannot ignite, or if they don’t stay lit, your furnace will have problems generating heat. Burners need airflow to ignite. The airflow comes from the blower fan pulling in the air.

If this airflow is hampered because of an issue with the blower or a clog in the furnace filters, the burners may not be able to ignite or stay lit for long. Most homeowners feel comfortable changing a dirty furnace filter. However, a faulty blower is something that will require the assistance of a professional HVAC technician.

Faulty flame sensors are another common reason why burners won’t stay on. A flame sensor is designed to keep you safe by ensuring that the gas coming through the burners is ignited. When the sensors do not detect flames, they automatically turn off the gas flow. Unburned gas won’t flood the combustion chamber and lead to a possible emergency.

If a flame sensor malfunctions, it may think that a burner is not ignited and shut the gas off. A dirty flame sensor requires professional cleaning, and a damaged unit must be professionally repaired or replaced.

Another safety feature that could affect your burners is the limit switch. This activates if the heat exchanger gets too hot by turning off the gas and power to the furnace.

The limit switch could be triggered if a clogged filter prevents sufficient air circulation from cooling down the heat exchanger, or it could be an issue with the furnace’s ability to vent combustion gas from the heat exchanger. Either way, you will want professional HVAC technicians to look at the problem as quickly as possible.


The air ducts are responsible for transporting warm air through the house and face wear and tear as they are often situated outside the heated part of the home. They are exposed to extreme temperature fluctuations throughout the year, leading to cracks or openings that allow the cold air surrounding your ducts to get in and the hot air to escape.

The outside air lowers the temperature of the air produced by the furnace, causing cooler air to circulate through your home. During your annual HVAC maintenance, our technicians will review your ductwork, identify places of potential weakness or damage, and offer actionable solutions.


A dirty, clogged filter may restrict the airflow to your furnace. This will limit the furnace’s ability to distribute warm air in your home. Your furnace might even have a built-in shut-off switch that activates when the furnace gets clogged and protects the burner from overheating or the blower from getting damaged. Furnace filters are cheap and easy to change. Replacing them can often solve furnace heating issues.


At Dragonfly Heating & Cooling, we do more than provide HVAC service. We help you identify the best option for your home and then guide you through the entire process. Our NATE- and NCI-certified technicians make the ideal team to help you with all of your HVAC needs.

Our services include heating and AC maintenance, installation, and repair. We are proud to offer UV lights, indoor air quality testing, and PTAC units. We work on existing and new construction. Contact Dragonfly Heating & Cooling today. Let us show you what makes us different than the rest.

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