10 Furnace Troubleshooting Tips: How to Fix Any Heating Issue

If you’re shivering and reaching for a blanket more than usual or notice the temp on your thermostat dropping, your furnace might need a little TLC. Try some furnace troubleshooting to fix the issue before it worsens. Here are 10 furnace troubleshooting tips to get your unit back up and running (and some clear signs that it’s time to call an HVAC pro). 

1. Make Sure Your Thermostat Is On

Some furnace problems turn out to be simple-to-fix thermostat issues. Go to your thermostat and ensure the setting is on "heat." Set the temperature at least three degrees higher than the room temperature to ensure it kicks on. If your thermostat is off, you may need to change the batteries or switch the power back on.

2. Check the Connection for Your Smart Thermostat

If you have a smart thermostat, ensure there is a wireless connection. Try restarting your thermostat if there isn’t a connection.

If you have consistent issues with your thermostat turning off, you may need to add a common "C" wire to run your smart thermostat. Without one, your thermostat could be drawing power from your existing circuits, leading to a lack of power. You can hire a local electrician to do the job or learn how to install a C-wire yourself.

3. Reconsider the Location of Your Thermostat

If the temperature in your home feels different than what's reflected on the thermostat, you may need to relocate your thermostat. The unit may be too close to exterior doors or heat (such as in the kitchen), which will impact how it measures the temperature throughout your home. An HVAC pro or electrician should assess your thermostat location and handle the move. 

4. Open and Clear Your Vents

Your furnace pumps hot air through your ductwork and vents in your home. If your furnace is working but your house still feels cool, check each vent throughout your home to ensure they are all open and clear of obstructions. Move any furniture or rugs that are covering vents. Your vents might be in the ceiling, floor, or walls. 

Even if you have unused rooms, keep the vents open. Blocked vents can cause duct leaks and excessive air pressure in your HVAC system, leading to breakdowns and costly repairs.

If your furnace takes in air through outdoor vents, make sure the vents are clear of debris, leaves, and snow. Remove any items that might be limiting airflow. 

5. Replace or Clean Your Furnace Filter

Clogged air filters restrict airflow and heat flow, making your furnace work harder. Turn off your furnace before checking your filter. The filter is often located near the blower on the side of the furnace in a slide-out rack (if you have a horizontal-facing unit) or near the top and bottom doors (if you have a vertical-facing unit). 

Pull out the filter to see if it's dirty. If light cannot pass through the filter, it’s time for a new filter or a cleaning. Exchange the filter for a new one of the same size and type. If you’re unsure which type to choose, take some time to research the best filter for your furnace. If you have a permanent filter, vacuum the dust and debris with a shop vac and rinse the filter with water. Let it air dry before placing it back in your furnace.

Change your filter or clean it once every three months to keep your furnace working smoothly all season. Do not run your furnace without a filter because it can harm your system and cause air quality problems inside your home.

6. Verify Power

Your furnace troubleshooting might lead you to a sneaky power issue. Check the power switch on your furnace (it often looks like a light switch). If it's flipped on but your furnace still isn't working, the circuit breaker might be the culprit. 

Go to your electrical panel. Make sure your hands and feet are completely dry before touching the electrical panel. If your furnace breaker is in the “OFF” position, switch it to the “ON” position. If it's already on, switch it off and then back on again to reset it. If a fuse blows or circuit trips when you turn the breaker back on, contact a local electrician to assess the issue.

7. Secure Furnace Front Panel

If your furnace's front panel door isn't completely closed, the unit won't turn on. This is an intentional safety precaution. Head to your furnace and ensure the front panel door is closed.

8. Inspect the Furnace Flame

You'll see a flame in the combustion chamber if you have an older natural gas furnace (models made before 2010). The flame should be a consistent blue flame. You likely have dirty burners if the flame is a color other than blue or if the flame is uneven. You'll need an HVAC pro to fix the issue because it's unsafe to handle without specific training. 

Newer furnace models, often those built after 2010, use electricity to ignite, so you won't see a flame or need to deal with it. 

9. Relight the Pilot Light

If your furnace has a flame (most gas furnaces made before 2010), it is lit by a pilot light. Sometimes, the pilot needs to be relit. Turn off the gas via the gas valve for 15 minutes. Then, turn the gas back on. Follow the manufacturer's manual for instructions on how to relight the pilot light on your furnace. There is often a knob on the bottom of the unit. You can relight it by turning it off, waiting 60 seconds, and turning it back on. 

You may have a dangerous leak if you smell gas at any point. If so, evacuate your house immediately, call 911, and call an emergency HVAC repair pro. 

If you have a furnace that ignites with electricity, call an HVAC pro if it’s not firing up. Electrical issues are too complex and hazardous to fix without the proper training.

10. Call a Local HVAC Pro

If you've tried the furnace troubleshooting tips in this guide and your furnace still isn't heating your home, call a local furnace repair pro to handle the issue. Resolving a furnace problem sooner leads to a warmer home and prevents a larger, more expensive repair. 

If you smell gas from your furnace, turn off your furnace, leave your home immediately and call 911. Contact a local furnace repair pro to fix the issue. Gas leaks can be lethal. 

If you hear hissing or banging noises coming from your furnace, you likely have an electrical issue, and you should call a local furnace repair pro immediately. An HVAC pro should always handle mechanical and electrical issues.