How to Repair a Furnace: Troubleshooting and Fixes

A broken furnace can leave you in the cold – literally. If your heating system stops working, you’ll want to figure out what’s wrong and fix it as soon as possible. Some furnace issues have simple DIY solutions, while others may require help from a professional.

This guide will help you troubleshoot the problem, try easy fixes, and know when to call for expert help.

Why Is My Furnace Not Working?

Several things can cause a heater to stop working. Here are some common reasons:

• Thermostat problems: Check your thermostat first. If it's too low, your furnace won’t turn on.
• Furnace door won’t close: If your furnace door won’t close, the safety switch may prevent it from turning on. This can happen because of a misaligned door, debris, or a faulty latch.
• Dirty or clogged air filter: A dirty filter blocks airflow, making your furnace work harder or shut down.
• Furnace blower not working: If you hear the furnace running but no warm air is coming out, the blower may be the problem. A dirty blower motor or a worn-out belt could be the cause.
• Furnace fan not working: The fan pushes warm air through your home. If it's not running, check the circuit breaker and make sure the fan setting is on “auto.”
• Pilot light or ignition issues: Older furnaces use a pilot light, while newer models have electronic ignitions. If the pilot light goes out, you’ll have to relight it. If your electronic ignition won’t start, you may need professional help.
• Gas supply or power issues: If you have a gas furnace, make sure it's getting gas and electricity. Check the gas valve to make sure it's open. For all furnace types, check the circuit breaker to see if it tripped. If the breaker switch is in the middle or off position, it likely tripped.

How to Repair a Furnace

If your furnace isn’t working, try these furnace repair tips before calling a professional:

1. Check and Adjust the Thermostat

Your thermostat controls when your furnace turns on and off. If it's not set correctly, your furnace won't run. Here’s how to troubleshoot your thermostat:

• Set the temperature a few degrees higher than the current room temperature to see if the furnace kicks on.
• If the thermostat isn’t responding, change the batteries.
• For programmable thermostats, check the schedule settings to make sure they match your needs.

If your thermostat is old or unreliable, consider upgrading to a smart thermostat for better efficiency and temperature control.

2. Make Sure the Furnace Door is Closed Properly

If your furnace won’t start, the access panel may not be fully closed. Many furnaces have a safety switch that prevents operation if the door isn’t securely latched. Here’s how to fix it:

• Check for obstructions like debris, wires, or insulation that might prevent the door from closing.
• Align the panel properly so that it fits securely against the furnace frame.
• Secure the latches or screws to keep the door firmly in place.
• Press gently on the door to see if the safety switch engages.
• Inspect the switch or latches for damage. If they’re faulty, they may need to be replaced.

3. Replace the Air Filter

A dirty air filter can cause your furnace to overheat and shut down. To replace the furnace filter, you’ll need to:

• Turn off the furnace before checking the filter.
• Locate the filter. It’s usually inside the return air vent or the furnace cabinet. Check your owner's manual if you’re unsure.
• Remove the old filter and inspect it. If it’s covered in dust and debris, it’s time for a new one.
• Insert the new filter in the correct direction. Most filters have arrows on the side that should point toward the furnace.
• Secure the cover (if applicable) and turn the furnace back on.

A clean filter helps your furnace run better and improves indoor air quality. Changing your air filter every one to three months can help keep your furnace in good shape.

4. Inspect the Circuit Breaker

Your furnace needs electricity to work, even if it runs on gas. Here’s how to check the circuit breaker:

• Find your home's electrical panel and check if the furnace breaker has tripped.
• If it has, flip it back on.
• If the breaker trips again soon after, there may be a deeper electrical issue that needs professional attention.

If your breaker keeps tripping, your furnace might be using too much power because of a failing part. Reaching out to a professional to assess and diagnose the issue may be your best bet.

5. Relight the Pilot Light

If you have a gas furnace with a pilot light and it goes out, your furnace won’t produce heat. If the pilot light is out, follow the steps below:

• First, turn off the gas for a few minutes before trying to relight it.
• Follow the manufacturer’s instructions carefully since doing it incorrectly can be dangerous. If you feel uncomfortable at all, call a pro.
• If the pilot light doesn’t stay lit, the thermocouple (a small sensor that shuts off the gas if the pilot light goes out) may need to be replaced.

If you have an electronic ignition that isn’t working, you may need a technician to inspect it.

6. Clean the Furnace Blower and Fan

Dust and debris can build up in your furnace’s blower and fan, making it less efficient. To clean these components, you’ll want to:

• Turn off the power to the furnace before cleaning.
• Use a vacuum or soft brush to remove dust from the blower motor and fan blades.
• Check for any loose or damaged wires that could be causing problems with the furnace.

Keeping the blower and fan clean helps your furnace run more smoothly and prevents unexpected breakdowns from happening.

When Should a Professional Fix Your Furnace?

If you’ve tried these troubleshooting steps and your furnace still won’t work, it’s time to call an HVAC technician.

You should also get professional help if you notice:

• A burning smell or a strange noise coming from the furnace.
• A furnace that turns on and off too often (this is called short cycling).
• No heat is being produced, even though the thermostat and power are set correctly.
• The pilot light is yellow instead of blue (this could mean a gas leak).

How Much Does It Cost to Repair a Furnace?

The cost of furnace repairs depends on the problem. Here are some average repair costs:

• Thermostat repair: $100 to $600
• Blower motor repair: $150 to $2,000
• Ignition system repair: $150 to $500
• Gas valve repair: $200 to $600
• Furnace filter replacement: $1 to $35

Does a Home Warranty Cover Furnace Repairs?

Yes, a home warranty can cover furnace repairs — but coverage depends on your plan. A First American home warranty with heating system coverage can help take care of repairs or replacements for covered furnace parts when they break down due to normal wear and tear.

If your furnace stops working, you can submit a service request online or by phone. A prescreened technician will diagnose the issue and handle the repair, potentially saving you hundreds of dollars on fixes.

With a home warranty, you won’t have to scramble to find a technician or deal with unexpected repair expenses. Instead, you’ll get reliable service when you need it most.

Save on Furnace Repairs With a Home Warranty

Keeping up with furnace maintenance can help prevent costly breakdowns. Change your air filter regularly, keep vents clear, and schedule routine inspections. If your furnace does stop working, follow the troubleshooting steps in this guide. And if a major repair is needed, consider a home warranty so you’re covered when your furnace breaks down.

Get a free quote today to see how a home warranty can protect your home’s heating system.

The contents of this article are provided for general guidance only. First American Home Warranty does not assume any responsibility for losses or damages as a result of using this information.

Please be aware that if you disassemble a covered system or item, it can invalidate your home warranty or manufacturer's warranty.