When the winter chill sets in, a functioning furnace isn’t just a luxury—it’s a necessity. Your furnace keeps your home warm and comfortable, but like any appliance, it can falter over time. Spotting the warning signs early can save you from costly repairs or even complete system breakdowns.
This guide will walk homeowners, DIY enthusiasts, and property managers through the most common furnace issues, ways to address them, and when to call in the pros. With proper maintenance and quick action, you can ensure your furnace runs smoothly throughout the colder months.
Common Furnace Repairs
Understanding the most frequent furnace problems can prepare you to diagnose issues early and take action before they escalate. Here are some of the usual suspects when a furnace starts acting up, along with practical solutions.
1. Clogged Air Filters
A clogged filter is one of the most common—and preventable—furnace problems. When filters get dirty, they restrict airflow, forcing your furnace to work harder. This inefficiency can increase energy costs and even cause your furnace to shut down completely to avoid overheating.
Solution:
Replacing the filter is simple. Check the condition of your filter monthly, and replace or clean it every 1-3 months, depending on usage. Regular maintenance will improve airflow, reduce strain on your system, and lower utility costs.
2. Dirty Flame Sensor
A dirty flame sensor will cause your furnace to start the ignition process, and the flames will come on for a few seconds, and then turn off. The furnace will do this over and over until it locks itself out. If your furnace is doing this, cleaning the flame sensor is very easy to do with minimal tools. Hop over to The DIY HVAC Guy youtube channel and use the channel search bar to search “flame sensor” and you will find several videos on how to do this repair yourself.
3. Thermostat Issues
Before assuming your furnace is the problem, check the thermostat. A malfunctioning thermostat—due to dead batteries, loose wiring, or dirt buildup—can disrupt heating cycles or prevent your furnace from starting altogether.
Solution:
- Ensure the thermostat is set to “HEAT.”
- Replace the batteries if the screen is blank or unresponsive.
- Gently remove the cover with a screwdriver and tighten any loose wiring. If you’re unsure, contact an HVAC technician to repair or replace the thermostat.
4. Loud Noises
Furnaces are usually quiet, but if you hear banging, rattling, or screeching sounds, it’s a red flag. These noises often indicate loose or broken parts or even mechanical failures.
Solution:
Pinpoint the source of the noise and call an HVAC technician to diagnose and fix the issue before it causes further damage. Ignoring these sounds can lead to bigger (and costlier) problems.
5. Failing Starting Mechanism
Newer furnaces rely on electrical ignitions, while older models use pilot lights to start the heating cycle. If the ignition system or pilot light fails, your furnace won’t heat properly—or at all.
Solution:
Malfunctioning ignitions or pilot lights require professional replacement. If your furnace still uses a pilot light and is older than 2010, consider upgrading to a newer, more efficient system.
6. Blower Motor Issues
The blower motor drives the fan that circulates warm air throughout your home. If the motor isn’t working, you might notice reduced airflow—or none at all.
Solution:
First, check for a tripped circuit breaker or blown fuse. If those aren’t the issue, call a technician to inspect or replace the blower motor.
7. Cracked Heat Exchanger
A cracked heat exchanger is a serious safety concern, as it can lead to carbon monoxide leaks. Signs include unusual smells, soot near the burners, or an orange/yellow pilot light instead of blue. This issue requires immediate attention.
Solution:
If you suspect a heat exchanger crack, shut off your furnace and contact a professional immediately. Consider installing carbon monoxide detectors throughout your home for added peace of mind.
8. Bad Limit Switch
The limit switch is a safety device designed to shut down your furnace when it overheats. This can go bad due to leaving dirty filters in place for prolonged periods. A malfunctioning limit switch can cause frequent shutoffs or a blower fan that runs constantly.
Solution:
Call an HVAC technician to inspect and replace the faulty limit switch to maintain safe furnace operation.
The Importance of Regular Furnace Maintenance
The best defense against costly furnace repairs is regular maintenance. Annual tune-ups with an HVAC technician can prolong your furnace’s lifespan, improve efficiency, and reduce the likelihood of unexpected breakdowns.
What Does Furnace Maintenance Include?
During a maintenance visit, a technician will:
- Inspect and clean the burners.
- Replace air filters.
- Test and inspect components such as the heat exchanger, blower motor, and limit switches.
- Perform safety checks to ensure the system is running smoothly.
Why Schedule Maintenance in the Fall?
Scheduling maintenance before winter begins ensures your furnace is ready for heavy use and gives you time to address any issues before temperatures drop.
When to Call a Professional
While many furnace problems, like changing filters or batteries, can be handled by homeowners, others require expert attention. If you notice persistent issues that basic troubleshooting doesn’t resolve, unusual noises, or safety risks like a cracked heat exchanger, it’s time to call in the pros.
Keep Your Furnace Running Smoothly
Proactive care is key to keeping your furnace running efficiently throughout the winter. By staying vigilant for signs of trouble and scheduling regular maintenance, you’ll enjoy a warm, comfortable home without the stress or expense of unexpected repairs.