Troubleshooting Guide: How to Fix a Furnace Not Working

When the cold winter months arrive, having a properly functioning furnace is vital for maintaining a comfortable and cozy home. However, there may come a time when you encounter the frustration of a furnace not working. Before panicking and calling a professional, it’s important to understand that several common issues can cause a furnace to malfunction. This troubleshooting guide will help you identify and resolve the issue, saving you both time and money in the process.

Signs That Your Furnace Is Not Working

Recognizing the signs of a malfunctioning furnace is crucial in addressing the issue promptly. Some common indications that your furnace is not working properly include:

Insufficient Heat: If you notice that your home is not reaching the desired temperature despite the furnace running, it may indicate a problem.
Strange Noises: Unusual noises such as banging, squealing, or rattling from your furnace can signify mechanical issues.
Frequent Cycling: If your furnace frequently cycles on and off, it may signal issues with the ignition or thermostat.
Foul Odors: Strange smells, such as a burning odor or a sulfur-like scent, may indicate a malfunctioning furnace.
Increased Energy Bills: When your energy costs have unexpectedly increased, your furnace might not be functioning efficiently.

Common reasons why a furnace may not be working

There are several potential reasons why your furnace may not be functioning properly. Before diving into specific troubleshooting steps, it’s helpful to have a general understanding of these common issues:

Lack of Power Supply

The power supply is one of the first things to check when your furnace is not working. Ensure the furnace is correctly connected to the power source and check that the circuit breaker has not tripped. If the circuit breaker has tripped, reset it and test the furnace to see if it operates correctly. If the issue continues, consider contacting an electrician to resolve any electrical problems.

Thermostat Issues

Sometimes, the issue may be with the thermostat rather than the furnace. Verify that the thermostat is set to the correct temperature and mode (heat). If the thermostat is battery-operated, replace the batteries and see if that resolves the issue. Additionally, ensure that the thermostat is not obstructed by any objects that may interfere with its functioning. If the thermostat still does not work properly, it might require repair or replacement.

Ignition Problems

If your furnace utilizes an electronic ignition system, it could experience difficulties igniting properly. A faulty ignition switch, a dirty or corroded ignition sensor, or a gas supply issue can cause this. If you suspect an ignition problem, it is best to leave the troubleshooting and repair to a professional technician who can safely handle the furnace’s gas components.

Clogged Air Filters

Air filters are essential for preserving the efficiency of your furnace. Over time, they can become clogged with dust, dirt, and debris, hindering airflow and diminishing the furnace’s heating capacity. Regular maintenance (changing or cleaning the air filters) can avoid these issues and extend the lifespan of your furnace.

Malfunctioning Fan Motor

The fan motor is responsible for circulating warm air throughout your home. If the fan motor malfunctions, you may experience weak or no airflow from your vents. A faulty motor, a broken belt, or an electrical problem can cause this. If you suspect a problem with the fan motor, it is best to seek professional assistance to avoid further damage to the furnace.

Furnace Repair – The Basics

Your furnace is one of the most crucial appliances in your home, especially if you live in a region with cold weather. It’s essentially what keeps your living space comfortable, alongside running water. So, swift diagnosis and repair become essential when it malfunctions, particularly during plummeting temperatures.

Many common furnace issues can be resolved without an expensive service call. Consider these eight straightforward solutions before shelling out significant funds and enduring a lengthy wait for a repair technician.

You can run through all eight checks in just a matter of minutes. While we illustrate for a gas-fired, forced-air furnace, most of these checks also apply to electric furnace systems and hot water boilers.

Check the Thermostat

Before jumping to conclusions about a furnace malfunction, please take a moment to troubleshoot the thermostat to ensure it’s correctly signaling the furnace to activate. Thermostats, particularly programmable ones, can be intricate, and the more features they have, the greater the potential for issues.

Check Thermostat Settings: Also ensure that the thermostat is set to “Heat” mode and not “Cool.”
Temperature Setting: Verify the temperature setting is higher than the current room temperature. Increase it by five degrees to see if the furnace activates.
Day, Time, and AM/PM Settings: Confirm the thermostat displays the correct day, time, and AM/PM settings.
Inspect Thermostat Wires: Trace the thermostat wires back to the furnace for any breaks, especially after recent remodeling. If you find a break, splice the wire back together and secure it with electrical tape.
Replace Battery: Replace the battery to prevent losing settings during a power outage, which can cause the thermostat to revert to default programming.
Clean and Check Thermostat: Open the thermostat and blow out dust or debris. Ensure it’s level, securely attached to the wall, and all wires are tightly connected.
Bypass Programming: If you can’t resolve programming issues, bypass them by manually setting the temperature with the up/down controls and then pressing the hold button to activate the furnace.

Following these troubleshooting steps, you can resolve issues with your thermostat before assuming there’s a problem with your furnace.

Check the Breaker and Shut Off Switches

It might seem surprising, but furnace technicians frequently discover that the only fix needed for a furnace is to flip the switch to turn it on. Look for a standard wall switch near the furnace—regardless of age or type, every furnace has one somewhere. Additionally, check the circuit breaker or fuse dedicated to the furnace. Ensure the front panel that covers the blower motor is firmly in place—there’s a push-in switch underneath that needs to be fully engaged for the furnace to function properly.

Change the Furnace Filter

A blocked furnace filter can cause the furnace to shut down. It’s a common issue, usually caused by dirty filters. Dust and debris restrict airflow, and if the filter becomes too clogged, the heat exchanger can overheat and trigger a shutdown, leaving your home chilly. If the blower is operational but no heat is produced, it’s time to replace the filter. A dirty filter also results in soot buildup on the heat exchanger, reducing furnace efficiency and lifespan.

Refer to the owner’s manual for the filter’s location and removal instructions. Inexpensive flat filters should be changed at least once a month, ensuring the arrow points toward the furnace. Pleated filters should be inspected monthly by holding them up to the light; if the light doesn’t pass through clearly, it’s time for a replacement. While manufacturers suggest pleated filters can last three months, households with pets, children, or significant dust should change them more frequently.

Before replacing the filter or adjusting the thermostat or furnace, remember to turn off the shutoff switch and fully lower or turn off the thermostat.

Make Sure the Gas Is On

If your gas furnace isn’t producing hot air, it could be due to a simple fix like a turned-off gas valve. Trace the gas line from the furnace to the meter and locate a perpendicular handle on the gas pipe. If you find one, turn it parallel to the pipe to restore gas flow. Additionally, older furnaces or boilers might have a pilot light. Remove the front panel and burner cover to check if it’s lit. These steps can help troubleshoot and repair your gas furnace.

Make Sure the Chimney Exhaust Flue Is Clear

Birds are occasionally attracted to chimneys’ cozy warmth and may accidentally get trapped in the exhaust flue. First, switch off the furnace and lower the thermostat completely to address this. Then, carefully dismantle the duct where it connects to the furnace and inspect for debris, including fallen birds. When reassembling, ensure you put the sections back in the same order and orientation as originally.

Flush Out Drain Lines

During the heating season, high-efficiency furnaces can produce significant amounts of water, often draining several gallons daily. The furnace may shut down if sediment or mold buildup restricts the drain lines. If the drain hose appears dirty, you can remove it and fill it with bleach and water (25% bleach) to address this issue. After letting it sit for several minutes, flush the hose to clear any obstructions.

Look for Blocked or Leaky Ducts

If your furnace is running but some rooms remain cold, ensure all room registers are fully open. Then, inspect accessible ductwork for any gaps or disconnections between sections or at branching points. Seal any gaps using specialized metal duct tape, avoiding standard cloth tape, which can degrade quickly and potentially exacerbate leaks. Additionally, ascertain the cause if your furnace is leaking water.

Inspect the ductwork for handles sticking out; these could be dampers or air conditioner bypasses. Make sure they are set to the open position.

Clean Leaves and Debris from Intake and Exhaust vents.

Ensure that your furnace’s intake and exhaust vent out from your house’s side remain unobstructed. Replace any screen mesh covering the pipes with a 1/2-inch mesh hardware cloth. If you notice ice clogging either pipe, it may indicate a larger issue within the system. Clear the ice and promptly contact a technician to diagnose the underlying problem.

Heat pump owners should regularly clear grass and leave from the outdoor compressor unit’s fins. Before the heating season begins, gently hose down the unit from the top to remove dirt and debris from the housing.

When to call a professional for furnace repair

Although many furnace problems can be addressed through troubleshooting, sometimes it’s best to consult a professional for assistance. If you have followed the troubleshooting steps outlined in this guide and your furnace still isn’t working, it’s time to call a certified HVAC technician. Additionally, if you encounter any issues that involve electrical components, gas supply, or major repairs, it is always safer to rely on the expertise of a professional. Attempting to fix complex problems without the proper knowledge and tools can cause further damage or even pose a safety risk to you and your home.

Preventive maintenance tips for a well-functioning furnace

Regular preventive maintenance is crucial to avoid the inconvenience of a furnace not working when you need it most. Here are some tips to keep your furnace in optimal condition:

Maintenance Tips to Prevent Furnace Issues

Regular maintenance can help prevent furnace malfunctions and extend the lifespan of your appliance. Here are some maintenance tips to keep your furnace in optimal condition:

Schedule Annual Inspections: Arrange for a professional technician to inspect and service your furnace annually. They can detect and address potential problems and issues before they escalate into significant problems.
Clean or Replace Air Filters: Replace your furnace’s air filters regularly, ideally every one to three months. This will ensure proper airflow and prevent dust and debris from accumulating in the system.
Keep Vents Clear: Ensure that furniture, rugs, or other items do not block the vents and registers in your home. Blocked vents can disrupt airflow and strain your furnace.
Check Thermostat Batteries: If your thermostat uses batteries, check them regularly and replace them as needed. This simple step can prevent thermostat malfunctions and ensure accurate temperature control.
Keep the area Around the Furnace Clean: Clear any debris, clutter, or flammable materials from the area surrounding your furnace. This will decrease the risk of fire hazards and allow for proper ventilation.

FAQs

Why is my furnace blowing cold air?

There could be several reasons for a furnace blowing cold air, including thermostat issues, a malfunctioning blower motor, or a problem with the heat exchanger. It’s best to consult a professional technician to diagnose and resolve the problem.

How often should I replace my furnace filter?

The frequency of filter changes varies based on factors like filter type and household allergens. Typically, disposable filters should be changed every one to three months, and reusable ones should be cleaned monthly.

Can I perform furnace repairs myself?

While homeowners can perform some troubleshooting steps, furnace repairs often require specialized knowledge and tools. It’s recommended that complex repairs be left to trained professionals to ensure safety and prevent further damage.

Why is my furnace making strange noises?

Unusual noises from a furnace can indicate various issues, such as a loose belt, worn-out bearings, or a faulty motor. These problems should be addressed promptly to avoid further damage and potential safety hazards.

Should I turn off my furnace when not in use?

It’s unnecessary to turn off your furnace when not in use, especially during the heating season. Modern furnaces are designed to operate efficiently and safely for extended periods. However, regular maintenance and periodic inspections are still recommended.

Conclusion

A furnace not working can be a frustrating problem, especially during the colder months. However, armed with the knowledge provided in this troubleshooting guide, you can diagnose and fix many common issues independently. By checking the thermostat, inspecting the air filter, troubleshooting the ignition system, testing the blower motor, and addressing other potential causes, you can save time and money by avoiding unnecessary professional repairs. Remember to prioritize safety and consult a certified HVAC technician for complex issues or if you are unsure about any aspect of furnace repair. With regular preventive maintenance, you can ensure a well-functioning furnace and a cozy home throughout the winter season.

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