Troubleshooting Rheem Furnaces: 15 Common Issues and Solutions ⋆ HVAC Alliance Expert (2025)

When it comes to home heating, Rheem furnaces are known for their reliability and performance. However, like any mechanical system, they are not immune to occasional malfunctions. Knowing how to troubleshoot these issues can save time and money, and get your furnace back up and running efficiently. In this comprehensive guide, we’ll cover the 15 most common Rheem furnace problems and provide clear, actionable solutions.

1. Furnace Not Turning On

One of the most frustrating issues with a Rheem furnace is when it simply won’t turn on. This problem can stem from various causes, but with a bit of troubleshooting, you may be able to identify the source. Here are some common steps to take:

Check the thermostat settings – Make sure your thermostat is set to the correct mode. If it’s not set to “heat,” your furnace won’t kick in. Also, ensure that the desired temperature is higher than the current room temperature. Sometimes, a simple adjustment is all it takes.
Examine the circuit breaker – Your furnace needs electricity to run, and if the circuit breaker has tripped, it will cut off power to the unit. Go to your electrical panel and check if the breaker connected to your furnace is in the “off” position. If it is, reset it by switching it back to “on.”

Inspect the power switch – Another often overlooked issue is the power switch for the furnace. It’s usually located near the unit itself, and it can be mistaken for a light switch. Ensure the switch is in the “on” position.
Call a professional technician – If these basic troubleshooting steps don’t resolve the issue, it’s best to contact a certified technician. They can diagnose more complex problems like faulty wiring, malfunctioning components, or gas valve issues, ensuring your furnace operates safely and efficiently.

2. Furnace Blowing Cold Air

If your Rheem furnace is blowing cold air instead of the expected warmth, this can be a sign of several potential issues. Here’s a deeper look into what might be causing the problem and how to address it:

Pilot light issues – If your furnace has a pilot light and it’s gone out, the system won’t be able to heat air properly. To fix this, locate the pilot light and relight it, carefully following the manufacturer’s instructions. If it continues to go out, there could be a problem with the thermocouple or gas supply, which may require professional attention.

Thermostat malfunction – Your thermostat controls the temperature in your home by signaling the furnace when to heat up. If it’s malfunctioning, it may not correctly sense the temperature, causing the furnace to blow cold air. Sometimes, recalibrating the thermostat or replacing faulty batteries can solve the issue. However, in some cases, you may need a new thermostat altogether.

Clogged air filter – A dirty or clogged air filter can significantly reduce airflow through your furnace, causing the system to overheat and trigger safety mechanisms. This can result in the furnace blowing cold air to prevent further damage. Regularly replacing or cleaning the air filter can restore normal function and improve efficiency.

Call a professional technician – If these solutions don’t resolve the issue, or if you’re unsure about attempting any of the fixes, it’s advisable to reach out to a certified technician. A professional can troubleshoot complex issues like faulty sensors, blower motor problems, or ductwork obstructions, ensuring your furnace returns to full functionality.

3. Furnace Short Cycling

Short cycling is a frustrating problem that occurs when your furnace turns on and off too frequently without completing a full heating cycle. This not only prevents your home from reaching a comfortable temperature but also increases wear and tear on your furnace, potentially leading to costly repairs and higher energy bills. Here are some common causes and solutions:

Dirty air filters – A clogged air filter can restrict airflow, causing your furnace to overheat. When this happens, the system’s safety mechanisms shut it off to prevent damage. This cycle repeats as the furnace restarts and quickly overheats again. Regularly replacing or cleaning your air filters can help prevent this issue and maintain proper airflow.

Oversized furnace – If your furnace is too large for your home, it can heat the space too quickly. This rapid heating can cause the furnace to shut off prematurely, leading to short cycles. Unfortunately, in this case, the best solution may be to replace the furnace with one properly sized for your home, which will improve both comfort and efficiency.

Malfunctioning thermostat – If your thermostat is faulty or inaccurately reading the temperature, it may cause the furnace to short cycle. The thermostat may be sending incorrect signals to the furnace, making it turn on and off inappropriately. Checking the thermostat for calibration or considering a replacement can often resolve the problem.

Call a professional technician – If short cycling persists despite troubleshooting, it’s crucial to contact a certified technician. A professional can assess deeper issues such as electrical problems, heat exchanger damage, or gas valve malfunctions, ensuring your furnace operates smoothly and efficiently.

4. Pilot Light Won’t Stay Lit

When the pilot light on your Rheem furnace won’t stay lit, it can be a frustrating and potentially dangerous issue. The pilot light is responsible for igniting the burners that heat your home, so it’s crucial to address the problem as soon as possible. Here are some common causes and solutions:

Faulty thermocouple – The thermocouple is a safety device that monitors the pilot flame. If the flame goes out, the thermocouple shuts off the gas supply to prevent gas leaks. However, if the thermocouple itself is faulty, it might mistakenly shut off the gas even when the pilot light is still burning. Replacing a malfunctioning thermocouple can usually resolve this issue.

Dirty pilot assembly – Over time, dirt, dust, and debris can accumulate in the pilot assembly, obstructing the flame and preventing the pilot light from staying lit. Cleaning the pilot assembly with a soft brush or compressed air can often fix the problem and restore normal operation.

5. Noisy Furnace Operation

Unusual noises coming from your Rheem furnace can indicate a variety of underlying issues. While some sounds are minor, others may signal the need for repair. Here’s what some common furnace noises might mean:

Banging sounds – If you hear a banging noise when your furnace kicks on, it could be due to the air ducts expanding and contracting as they heat up and cool down. While this is generally harmless, it can also indicate delayed ignition, where gas builds up before the burners ignite, leading to a small explosion. This should be addressed promptly to avoid damage.

Rattling noises – Rattling sounds are often caused by loose screws, panels, or other components within the furnace. As the system operates, vibrations can shake these parts loose. Tightening any loose panels or screws can usually resolve the issue. However, persistent rattling may point to more serious internal issues.

Squealing sounds – A high-pitched squealing noise often signals an issue with the blower belt. The belt may be loose, worn, or damaged and might need adjusting or replacing. If left unaddressed, this can lead to more significant blower motor issues.

Call a professional technician – If the noise continues despite basic troubleshooting, it’s best to contact a certified technician. They can diagnose more complex issues such as motor failure or problems with the heat exchanger, ensuring your furnace is safe and efficient.

6. Ignition Problems

If your Rheem furnace isn’t igniting properly, it can stop the system from producing heat, leaving your home cold and uncomfortable. Here are some common reasons for ignition problems and how to address them:

Check the ignition switch – A faulty ignition switch can prevent your furnace from lighting. If the switch is worn out or damaged, it may need to be replaced. Be sure to inspect the switch for any visible damage and consult the furnace manual for replacement instructions.

Gas supply issues – If the furnace isn’t getting gas, it won’t ignite. First, check to make sure the gas valve is open and that gas is flowing to the furnace. If the gas valve is closed or if there’s an issue with the gas line, the furnace won’t be able to operate.

Dirty burner – Over time, dust and debris can accumulate on the burner, obstructing the flow of gas and preventing proper ignition. Regularly cleaning the burner ensures that the system ignites smoothly. If you notice the flame sputtering or going out quickly, a dirty burner may be the cause.
Call a professional technician – If ignition problems persist, it’s essential to contact a certified technician. A professional can inspect and repair complex issues like faulty ignition switches, gas valve malfunctions, or burner defects, ensuring safe and reliable furnace operation.

7. Blower Motor Not Running

The blower motor in your Rheem furnace plays a crucial role in distributing warm air throughout your home. When it stops functioning, your furnace may produce heat, but it won’t be able to circulate it. Here are some common causes of blower motor failure and how to address them:

Blown fuse – If the blower motor isn’t running, a blown fuse in the furnace’s control board might be the issue. The fuse protects the motor from electrical overloads, and when it blows, the motor won’t operate. Replacing the blown fuse with the correct type can restore the motor’s functionality.

Worn-out motor – Like any mechanical component, blower motors can wear out over time, especially with extended use. If the motor is making grinding or humming noises, or if it fails to turn on altogether, it may need to be replaced. A malfunctioning motor is typically beyond repair and requires a new unit to ensure efficient heating.

Clogged air filter – A clogged air filter can obstruct airflow, putting extra strain on the blower motor. Over time, this stress can cause the motor to overheat and shut down. Regularly changing or cleaning the air filter can prevent this issue and ensure the blower motor runs smoothly.

Call a professional technician – If the blower motor continues to malfunction despite troubleshooting, it’s wise to contact a certified technician. They can diagnose deeper electrical or mechanical issues, such as motor capacitor failure or wiring problems, ensuring your furnace distributes heat efficiently and reliably.

8. Furnace Turns Off Too Soon

If your Rheem furnace turns off before your home is fully heated, this is known as short cycling. It can lead to uneven temperatures and strain on the system. Here are some common causes and how to address them:

Overheating – If your furnace overheats, it will shut off as a safety measure. This can happen when airflow is restricted, often due to a dirty or clogged air filter. Replacing or cleaning the air filter can help maintain proper airflow and prevent overheating, allowing the furnace to complete its cycle.
Thermostat placement – If your thermostat is installed near a heat source, such as a vent, radiator, or sunlight, it may sense higher temperatures than the rest of the home. As a result, it will signal the furnace to shut off before the entire house is warmed. Relocating the thermostat to a more central location can resolve this issue. Additionally, if you suspect issues with the thermostat itself, consider thermostat repair to ensure accurate temperature readings and proper furnace operation.

Blocked airflow – If vents or ductwork are blocked by furniture, debris, or other obstructions, airflow becomes restricted. This can cause the furnace to overheat and shut down early. Ensuring that vents and ducts are clear will help your furnace operate more efficiently and complete its heating cycle.

Call a professional technician – If your furnace continues to turn off prematurely, it’s best to consult a certified technician. They can identify more complex issues such as malfunctioning limit switches, faulty thermostats, or ductwork problems, ensuring your furnace runs efficiently and safely.

9. Furnace Producing Burning Smell

A burning smell coming from your Rheem furnace can be concerning, but it doesn’t always indicate a serious problem. However, it’s essential to identify the cause to ensure your safety and prevent damage to your furnace. Here are some potential reasons:

Dust burning off – If your furnace hasn’t been used for a while, especially at the beginning of the heating season, dust can accumulate on the heat exchanger or other internal components. When the furnace is turned on, this dust burns off, producing a temporary burning smell. This odor should dissipate after a few minutes, but if it persists, further inspection may be necessary.

Electrical issues – A burning smell that lingers or smells like burning plastic could point to an electrical problem. Frayed wires, malfunctioning components, or an overheating motor can all cause this odor. Electrical issues pose a fire hazard, so it’s essential to turn off the furnace immediately and avoid using it until a professional has inspected it.

Overheating – If your furnace is overheating, it can produce a burning smell as components get too hot. This can happen due to restricted airflow, often caused by a dirty filter or blocked vents. Check the air filter and replace it if necessary to ensure proper airflow. Overheating is a safety concern, so it should be addressed promptly.

Call a professional technician – If the burning smell persists or you suspect an electrical or overheating issue, it’s important to contact a certified technician. They can inspect the furnace for potential hazards, such as electrical malfunctions or overheating components, and ensure that your furnace is operating safely.

10. Thermostat Not Communicating with Furnace

When your thermostat isn’t communicating with your Rheem furnace, it can result in erratic heating, or the furnace may not turn on at all. Here are some common causes of this issue and how to resolve them:

Check the wiring – Loose or damaged wires can prevent proper communication between the thermostat and the furnace. Over time, connections can become loose or wires can fray, disrupting the signal. Inspect the wiring to ensure everything is properly connected and intact. If you notice any damage, it’s crucial to fix or replace the wires to restore communication.

Low battery – Many thermostats, particularly digital or programmable models, rely on batteries to function. If the battery is low, it may cause the thermostat to behave unpredictably or stop communicating with the furnace altogether. Replacing the batteries is a simple fix that can restore normal operation.

Replace the thermostat – If the thermostat is old, malfunctioning, or unresponsive, it may need to be replaced. An outdated or faulty thermostat can misread temperature settings or fail to send the correct signals to the furnace. Upgrading to a new, more efficient model may resolve these issues and improve overall heating performance.

Call a professional technician – If wiring issues persist or replacing the thermostat doesn’t solve the problem, it’s best to contact a certified technician. They can perform a thorough inspection to identify and fix more complex communication problems between the thermostat and the furnace.

11. Furnace Fan Not Working

If the furnace fan isn’t operating, your Rheem furnace won’t be able to circulate warm air throughout your home, even if the system is producing heat. Here are some common causes of this issue and potential solutions:

Check the limit switch – The limit switch monitors the furnace’s internal temperature and controls when the fan turns on and off. If the limit switch is malfunctioning, the fan may fail to start even though the furnace is producing heat. Replacing a faulty limit switch can restore the fan’s functionality and ensure proper air circulation.

Blower motor failure – The blower motor powers the fan that distributes air through your ductwork. If the motor is defective or worn out, the fan won’t run, leaving your home without adequate heating. In many cases, a malfunctioning blower motor will need to be replaced to get the system back up and running.

Clogged air filter – A dirty or clogged air filter can restrict airflow, making it difficult for the fan to operate efficiently. When the furnace’s airflow is obstructed, the fan may stop working properly. Regularly changing or cleaning the air filter can prevent this issue and keep the fan running smoothly.
Call a professional technician – If the fan continues to malfunction despite basic troubleshooting, it’s best to consult a certified technician. They can inspect the limit switch, blower motor, and other components to accurately diagnose the problem and ensure your furnace operates efficiently.

12. Heat Exchanger Problems

The heat exchanger is one of the most vital components of your Rheem furnace, responsible for transferring heat to the air that circulates through your home. Problems with the heat exchanger can pose serious risks, both to your furnace’s efficiency and to your safety. Here are some common heat exchanger issues to watch out for:

Cracked heat exchanger – A cracked heat exchanger is one of the most dangerous issues your furnace can face. When cracks form, they can allow carbon monoxide (CO) to leak into your home. Carbon monoxide is a colorless, odorless gas that can be life-threatening if inhaled in large amounts. If you suspect a crack in your heat exchanger, turn off your furnace immediately and contact a professional to inspect and address the issue.

Rust or corrosion – Over time, moisture buildup inside the furnace can lead to rust or corrosion on the heat exchanger. This corrosion weakens the metal, reducing the heat exchanger’s efficiency and potentially leading to complete failure. Regular furnace maintenance can help prevent rust from forming, but if corrosion is already present, it may require repair or replacement of the heat exchanger.

Call a professional technician – Given the potential safety hazards associated with heat exchanger problems, it’s crucial to have a certified technician inspect your furnace regularly. If you notice any signs of a cracked or corroded heat exchanger, they can perform the necessary repairs or replacements to keep your system running safely and efficiently.

13. Furnace Not Blowing Enough Heat

If your Rheem furnace is running but isn’t producing enough heat to keep your home warm, there could be a few underlying issues. Here are some common reasons for inadequate heating and how to address them:

Blocked air vents – One of the simplest causes of insufficient heat is blocked or closed air vents. Ensure that all vents throughout your home are fully open and unobstructed by furniture or other items. Proper airflow is essential for distributing warm air evenly throughout your space.

Dirty air filter – A clogged air filter can severely restrict airflow, making it difficult for your furnace to heat your home effectively. The reduced airflow puts extra strain on the system and limits the amount of warm air being circulated. Regularly cleaning or replacing the air filter can help improve airflow and heating efficiency.

Undersized furnace – If your furnace is too small for your home’s heating demands, it may struggle to generate enough heat. An undersized furnace will run longer than necessary without adequately heating the space, leading to high energy bills and discomfort. In this case, upgrading to a properly sized furnace may be the best solution.

Call a professional technician – If your furnace continues to struggle with producing enough heat despite troubleshooting, it’s essential to contact a certified technician. They can assess the system, check for mechanical issues, and recommend the right solutions to ensure your home stays warm and comfortable.

14. Furnace Running Constantly

If your Rheem furnace is running nonstop without cycling off, it could be a sign of inefficiency or malfunction. Here are some potential causes and solutions for this issue:

Thermostat settings – Check your thermostat settings to ensure it is set to “auto” instead of “on.” When the thermostat is set to “on,” the furnace fan will run constantly, regardless of whether the system is heating. Setting it to “auto” allows the furnace to cycle on and off based on the temperature setting, conserving energy.

Faulty limit switch – The limit switch is responsible for regulating when your furnace turns on and off. If the limit switch is malfunctioning, it may fail to signal the furnace to shut down, causing it to run continuously. A faulty limit switch will often need to be replaced to restore proper function.

Leaky ductwork – If there are leaks in your ductwork, warm air may be escaping before it reaches your living spaces. This forces the furnace to work harder and run continuously to maintain the desired temperature. Sealing ductwork leaks can help resolve this issue and improve the overall efficiency of your heating system.

Call a professional technician – If your furnace continues to run constantly despite adjusting the thermostat and checking for leaks, it’s a good idea to call a certified technician. They can inspect the furnace and thermostat for any mechanical or electrical problems, ensuring the system operates efficiently and cycles off as needed.

15. Dirty Flame Sensor

The flame sensor is a critical component in your Rheem furnace, responsible for detecting whether the furnace has successfully ignited. If the flame sensor is dirty or malfunctioning, it can prevent the furnace from lighting properly and result in gas buildup. Here’s how to address issues with a dirty flame sensor:

Clean the sensor – A common cause of ignition problems is a dirty flame sensor. Over time, dust and residue can accumulate on the sensor, leading to inaccurate readings and preventing the furnace from igniting. Cleaning the sensor with fine steel wool or a soft brush can remove the buildup and restore proper function. Be sure to turn off the furnace and allow it to cool before cleaning the sensor.
Replace the sensor – If cleaning the flame sensor doesn’t resolve the issue, it may be defective and require replacement. A faulty sensor will continue to misread flame detection, causing repeated ignition failures. Replacing the sensor is typically a straightforward process, but ensuring the correct part is installed is crucial for safe and efficient operation.

Call a professional technician – If you’re unable to resolve the issue with cleaning or replacing the flame sensor, or if you’re unsure about performing the repair yourself, it’s wise to contact a certified technician. They can accurately diagnose and address any issues with the flame sensor or other components, ensuring your furnace operates safely and efficiently.

Who Should I Call for HVAC Repair Services?

For any ongoing issues with your Rheem furnace, it’s essential to seek professional assistance to ensure your system operates safely and efficiently. HVAC Alliance Expert is ready to help diagnose and resolve complex problems with expert care. Their certified technicians can address any furnace issues, from ignition problems to heat exchanger concerns, ensuring your home stays warm and comfortable. Contact HVAC Alliance Expert today for reliable and thorough HVAC repair services—your comfort is their top priority!

Conclusion

In conclusion, troubleshooting Rheem furnace issues can help restore comfort and efficiency in your home. From addressing common problems like pilot light failures and short cycling to dealing with more complex issues such as heat exchanger cracks, timely maintenance and professional assistance are key. For persistent or intricate furnace issues, it’s best to rely on a certified technician. HVAC Alliance Experts offer expert furnace repair services to ensure your furnace operates smoothly and safely. Reach out today for reliable HVAC solutions.

FAQs

What should I do if my Rheem furnace won’t turn on?

Check the thermostat settings, ensure the circuit breaker is on, and inspect the power switch. If these steps don’t help, contact a certified technician for further diagnosis.

Why is my Rheem furnace blowing cold air?

Possible causes include a pilot light issue, malfunctioning thermostat, or a clogged air filter. Re-light the pilot, check the thermostat, or replace the filter to address the problem.

How can I fix short cycling in my Rheem furnace?

Short cycling can often be caused by dirty air filters, an oversized furnace, or a faulty thermostat. Replace the filter, ensure the furnace is correctly sized, or recalibrate the thermostat to resolve the issue.

What should I do if my furnace is producing a burning smell?

A burning smell might be due to dust burning off, electrical issues, or overheating. If the smell persists, turn off the furnace and contact a professional technician for a thorough inspection.

What could cause my furnace fan to stop working?

Common causes include a faulty limit switch, blower motor failure, or a clogged air filter. Check and replace these components as needed, and consult a technician if the issue persists.