Before troubleshooting your furnace, it helps to understand its basic operation. A furnace generates heat through combustion, where fuel is burned to create heat inside a heat exchanger component. The heat exchanger then transfers this heat to the air that circulates through your home via the blower. If your furnace starts blowing cold air, something is disrupting this process. Common causes include issues with fuel supply, ignition, or airflow. Having a basic understanding of your heating system helps you identify basic problems you may be able to address or describe the issue to your HVAC technician for more effective troubleshooting.
Thermostat Issues
Thermostats act as the central control for your furnace. They regulate your home’s temperature by turning your furnace on and shutting it off to achieve the temperature you have set.
If cold air is coming from your vents, the first step is to ensure your thermostat is set to heating mode. Many thermostats have a fan-only setting to provide ventilation without heating or cooling your home’s air. The set temperature must also be warmer than the ambient room temperature, or the furnace will not turn on.
If you still have an issue after ensuring that the thermostat is in heating mode and the temperature is set correctly, resetting your thermostat according to the manufacturer’s instructions can often resolve the problem.
Alternatively, your thermostat may not accurately read your home’s temperature. To test it, tap a reliable thermometer on the wall next to your thermostat. Wait about 15 minutes, then compare the two readings. If they are within a few degrees, your thermostat is reading the temperature correctly. You will need the help of a professional if the thermostat needs to be recalibrated. They can also diagnose and fix other issues, like faulty wiring interfering with your thermostat’s communication with your furnace.
Clogged Filter
Among a host of other issues, a clogged furnace filter can cause cold air to come from your home’s vents. The filter prevents dirt and debris from entering your heating system and causing damage to its internal components. It also plays an essential role in maintaining indoor air quality by capturing airborne contaminants that would otherwise recirculate through your home. However, when a filter becomes clogged, airflow through your furnace is reduced. This reduced airflow can cause the system to overheat, triggering the furnace’s safety features, which shut it down to prevent damage. Depending on your system’s setup, the blower fan may continue running, pushing unheated air through your vents.
Experts recommend changing your furnace’s filter at least every three months. However, you may need to replace yours more often based on factors like how frequently your system runs, if you have pets and how many people live in your household. You may also need to replace your filter more often if you use high-quality filters because a family member has respiratory issues. Many homeowners check their heating system’s filter once a month to determine when it needs to be changed out.
Pilot Light or Ignition Problems
Furnaces that run on natural gas or heating oil depend on either a pilot light or an electronic ignition system to ignite the burners and produce heat. If the pilot light goes out or the ignition system fails, the furnace won’t generate heat and will blow cool air instead.
Common signs of pilot light issues include a flickering flame, no flame, or a yellow flame, indicating incomplete combustion. If you notice any of these signs, it’s essential to contact a professional to diagnose and fix the problem. Ignoring these signs can lead to more severe issues, including a dangerous carbon monoxide leak.
Alternatively, common problems with electronic ignition systems include dirty sensors or faulty components. A HVAC technician may be able to solve the problem by cleaning the sensor, but may need to replace your ignition system.
Limit Switch Problems
Furnaces have a limit switch that prevents them from causing a fire if they overheat. However, like any other component, the switch can malfunction and shut down your furnace even if your heating system is operating safely. A professional can determine if the switch is triggering because there is a serious issue causing your furnace to get too hot or if it just needs to be replaced.
Fuel Supply Issues
A steady gas or oil supply is essential for your furnace to function correctly. Any disruption to this fuel source will prevent the furnace from heating the air and cause it to blow cool air instead.
Several issues can affect the fuel supply to your furnace. For instance, fuel lines can become blocked, or you may have a faulty thermocouple. The thermocouple detects whether the pilot light is lit and regulates fuel flow accordingly. Additionally, dirty burners can cause ignition delays.
To restore your furnace’s operation, a technician will check for consistent fuel flow, inspect components like the thermocouple and burners, and repair any issues.
Condensate Drain Clogs in High-Efficiency Furnaces
If you have a high-efficiency furnace, a clogged condensate line can cause it to shut down for safety. As moisture backs into your heating system, it triggers the float switch, which shuts off the unit. To address this issue, a technician will disassemble your furnace’s drainage system and clean out the condensate line and drain pan.
How Do HVAC Technicians Troubleshoot Furnaces?
HVAC technicians use a systematic approach to diagnose and troubleshoot furnace issues. The process usually begins with gathering information from the homeowner, including details about the system’s symptoms, maintenance history, and age. Providing as much information as possible helps technicians identify potential problems more quickly.
The next step involves checking the furnace’s power and gas supply to ensure everything is operating as it should. Technicians will also test the system’s electrical continuity, which involves checking all connections and circuits for proper function. A comprehensive inspection, along with performance testing, allows them to pinpoint the source of the problem and identify any necessary repairs.
Once repairs are completed, your technician will conduct further system testing. This ensures that the furnace cycles on and off correctly, heats your home as expected, and maintains adequate airflow throughout the system. Technicians may also calibrate your furnace to optimize performance and ensure it runs efficiently. This step can reduce your monthly heating costs.
It’s important to rely on professional HVAC technicians for troubleshooting and repairs, as the process can be hazardous without the proper expertise. With years of training and experience, technicians can safely and effectively handle diagnostics and repairs, ensuring your furnace functions efficiently.
Contact Your Local Professionals
At Magic Electric, Plumbing, Heating + Air, we have been serving the residents of Twin Falls, ID, and the surrounding areas with heating and cooling services for years. We install, repair, and maintain heating and cooling systems. Additionally, we can help with all your electrical needs, including installing electric vehicle charging stations, generators, and whole-home surge protection. As your one-stop homecare provider, we also provide plumbing services. Contact us today to schedule a heating appointment with one of our experienced team members.
