10 Most Common Furnace Repairs
Learn about the most common furnace repairs so you can avoid a complete breakdown and keep your home warm and cozy all winter.
By Tom Moor
As the chill of winter sets in, the last thing you want to worry about is your furnace. A malfunctioning heater can quickly turn cozy nights into uncomfortable ones, especially when temperatures drop. The good news is that by spotting warning signs early – like strange noises, clogged filters, or thermostat issues – you can often avoid bigger, costlier repairs.
Keep reading as we discuss the 10 most common furnace repairs to watch for and how regular maintenance can help keep your system running smoothly all winter long.
Frequent furnace issues and how to solve them
1. Clogged air filters
Out of sight and out of mind, many homeowners simply forget to change their system’s air filter on a regular basis. Big deal, right? Unfortunately, it is, as clogged filters can lead to a host of issues. When air filters become clogged with contaminants, it can significantly reduce airflow into the system which can lead to system wear and tear, higher energy costs, and even a complete shutdown to prevent overheating.
Solution: Fortunately, this is a relatively simple fix. A good rule of thumb is to check the filter’s condition every month and replace it when it looks dirty, typically every 2-3 months.
2. Short cycling
Short cycling occurs when your furnace turns on and off too frequently without fully heating your home. Furnace short cycling is caused by clogged air filters, malfunctioning thermostats, and oversized furnaces that heat the space too quickly. Short cycling is a serious issue that can lead to increased energy bills, reduced system efficiency, and potential damage to components over time.
Solution: Start by checking the filter and replace it if it’s clogged. If that’s not the problem, contact an HVAC technician to take a closer look. They can determine if your furnace is oversized or whether another underlying issue is at play.
3. Pilot light or ignition problems
Older furnaces with a pilot light or newer models with an electrical ignition both rely on these components to start the heating cycle. If your furnace isn’t heating properly, one of these parts may not be working properly. This can happen due to wear and tear over time, or because of dirt buildup, a dirty air filter, a clogged gas line, or a malfunctioning sensor.
Solution: For older furnaces, a faulty pilot light might require replacing the entire system, especially if it’s an outdated, inefficient model. For newer units, an HVAC technician can replace the ignition system to get your furnace up and running again.
4. Strange noises
Furnaces that are working properly are relatively quiet. If you’re losing sleep due to strange noises such as rattling, banging, or squealing sounds, a mechanical issue or a broken part could be the culprit.
Solution: Leave loud furnace noises to a professional HVAC technician to prevent any further damage.
5. Cracked heat exchanger
A cracked heat exchanger should not be taken lightly. Not only does it cause inefficiency, but it can leak carbon monoxide, which is a dangerous, odorless gas that can be fatal if inhaled in high concentrations. Signs of a cracked furnace heat exchanger include a yellow or flickering pilot light, unusual smells, and soot around the furnace burners.
Solution: Turn off your furnace immediately and call a qualified HVAC technician. They may recommend replacing just the heat exchanger if the furnace is less than 10 years old and the rest of the components are in good condition. However, if the unit is old or has other issues, the technician might suggest replacing the entire furnace for long-term efficiency and safety.
6. Thermostat issues
Sometimes the issue isn’t with the furnace itself, but with the thermostat that’s controlling it. Dirty sensors, loose wires, or dead batteries are all potential causes of a malfunctioning thermostat that can cause your furnace to work intermittently or not at all.
Solution: It’s possible someone accidentally bumped into the thermostat in the middle of the night and changed its setting. Make sure the thermostat is set to HEAT and increase the temperature a couple of degrees to see if it starts up. If the screen is blank, check if the batteries need to be replaced.
If neither works, you can inspect the wiring or contact a professional to repair or replace the thermostat. You can also try some of the tips on our thermostat troubleshooting page.
7. Blower motor malfunctions
A furnace blower motor powers the fan that circulates warm air from the furnace through the ductwork and into your home. If it’s not working correctly, you’ll notice poor airflow or a blower that won’t turn on at all, leaving your house feeling cold and uncomfortable.
Solution: If your blower motor isn’t starting, check for a tripped circuit breaker or blown fuse. If these aren’t the issue, call a professional to inspect or replace the motor before it leads to further issues with your furnace. A furnace blower motor may need to be replaced if it becomes worn out, develops electrical issues, or fails to operate efficiently.
8. Dirty or broken flame sensor
A dirty or broken flame sensor can cause your furnace to shut down too soon or prevent it from starting altogether. Located near the burner, the flame sensor’s job is to detect the presence of a flame. If it’s dirty or faulty, the furnace may think there’s a problem and shut off to avoid safety risks.
Solution: A professional can clean or replace the flame sensor to ensure the furnace operates properly, preventing unnecessary shutdowns.
9. Tripped circuit breaker or blown fuse
A tripped circuit breaker or blown fuse can disrupt the flow of electricity to your furnace, preventing it from turning on. This electrical issue is often caused by an overload in the system, airflow issues, or furnace electrical problems, causing the breaker to trip or the fuse to blow.
Solution: Check the circuit breaker or fuse box and reset the breaker or replace the blown fuse. If the problem persists, reach out to an HVAC technician to inspect the electrical components of your furnace.
10. Gas valve issues
The gas valve controls the flow of natural gas into the furnace’s burner, and if it’s malfunctioning or not opening correctly, the furnace won’t receive the fuel it needs to produce heat. This can result in the furnace failing to start or shutting down unexpectedly.
Solution: If you're having issues with your furnace gas valve, first check that the power is off and the gas supply is turned off for safety. It’s best to contact a certified technician to diagnose and repair the problem, as dealing with gas valves requires professional expertise to prevent hazards.
Regular maintenance can prevent furnace breakdowns
If you’re looking to keep your furnace running efficiently while preventing costly breakdowns, it’s important to invest in an annual furnace tune-up. During a tune-up, a technician will clean key components, lubricate moving parts, check the thermostat, inspect the blower motor, and replace the air filter if needed. This improves energy efficiency and helps catch potential issues before they become major problems.
Regular furnace maintenance also extends the lifespan of your furnace, ensuring it operates safely and reliably. By addressing minor concerns early, you can avoid expensive repairs and reduce the risk of dangerous issues, like carbon monoxide leaks. In the end, a yearly tune-up provides peace of mind and keeps your home warm all winter long.
Schedule furnace maintenance or repair
Don’t let furnace issues spoil a cozy evening at home this winter. A local American Standard® dealer can provide the maintenance and repairs your system needs to ensure it’s ready to tackle another heating season.
Author: Tom Moor
Expert review by Kimberly Sexton, Senior Systems Engineer
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