Thermostat Says Heat On but Furnace Not Running

If your nose is cold and your teeth are chattering in your own home, there’s a problem. The first thing you do is go look at the thermostat to see if it somehow got turned off. But no, there it is, saying it is in heating mode.

Before assuming the worst – that your gas furnace is failing – take some time to make sure your HVAC thermostat isn’t the culprit. Try these troubleshooting tips to fix the problem:

Loose or damaged wiring may be to blame for the thermostat not turning on the heat. You can remove the faceplate or front of a thermostat to make a visual inspection but don’t touch the wires. If you see damage, call an electrician or HVAC company to replace the wiring. Now might also be a good time to replace the thermostat if it’s old.

If applicable, try replacing the thermostat batteries. Dying batteries can cause the thermostat to act strangely. Some thermostats give a warning of low battery. Don’t ignore the warning. To prevent issues in the future, replace the batteries once a year.

While you have the thermostat cover off, check for accumulated dirt and grime. This can be a problem for an old thermostat with a removable cover. Use a clean paintbrush or makeup brush to gently brush away dust and dirt. You can use something thin like a piece of paper to help remove debris that is stuck between components.

If you did a DIY thermostat installation recently or someone else recently installed it, it might have been installed incorrectly. If you have a heat pump system, ensure you have a compatible heat pump thermostat. Consult with an HVAC pro to assess the situation.

If your thermostat says heating but the furnace is not on and you’ve tried the thermostat troubleshooting tips, the thermostat may not be the problem. Other possible causes include:

• Dirty furnace filter/restricted airflow
• Furnace power switch is off
• Tripped circuit breaker
• No gas supply
• Bad blower motor
• Dirty furnace ignitor

Check out our furnace troubleshooting tips for when the furnace is not turning on. Be prepared to call an HVAC company for help getting your heating system up and running.

If your thermostat is not turning on the heat or your furnace is on the fritz, stop shivering and call your local Trane dealer for help. If it’s a Trane smart thermostat that is connected to the internet and you have granted Trane Diagnostics remote access, they may be able to troubleshoot the issue and fix it remotely.

If you need a new thermostat or furnace repair, they can also schedule an on-site visit to get your furnace working as it should.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

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