Furnace Not Turning On

Whether the first chilly day or night is here or winter is here with a vengeance, you expect your furnace to comfortably heat your home. But what do you do when the furnace is not kicking on when the temperature drops? If your furnace doesn’t turn on when you want it to, it’s time to do some investigating.

There are multiple reasons why your furnace is not coming on. They include:

• Human error 
• Faulty thermostat
• Tripped circuit breaker
• Airflow issues
• Gas supply or valve issues
• Faulty igniter

Let’s explore these causes and potential fixes for when your furnace is not working.

If your gas furnace is not working, there are some simple furnace troubleshooting steps you can take. If they don’t solve the problem, call an HVAC professional.

Before you call for furnace repair, ensure the thermostat is set to “Heat” and the temperature inside is colder than what you have the desired temperature set at. If the furnace is not turning on automatically when it should, check to make sure you have the thermostat set correctly.

While some thermostats will have the furnace come on automatically, others require you to toggle the switch or press a button.

Another reason for your gas furnace not working is a faulty thermostat. If the thermostat says the heat is on but the furnace is not running, check for an error code on a programmable thermostat and follow the thermostat troubleshooting tips in your owner’s manual. 

If you have a thermostat that uses batteries, replace the batteries. If it’s hard-wired, check for loose wiring. If you’re satisfied that the thermostat is not the problem, continue with the next troubleshooting steps.

Even though your furnace burns natural gas, it uses electricity to start and run the motor and blower fan. Look for something similar to a light switch on the side of the furnace, on a nearby wall, or ceiling joist. Make sure it’s in the “On” position. 

Check the circuit breaker box for a tripped breaker switch. If you don’t know where it is, look for a grey or green metal door in the wall in your basement, garage, or utility room. Open it and look for a switch that is tripped. Toggle it back to On and see if the furnace starts up. If the circuit trips again, you have an electrical issue. Call your HVAC company for help.

Your furnace needs good air circulation throughout your home to operate. Check the air filter and change it if it looks dirty or you can’t remember when you changed it last. Make sure you don’t have any couches, chairs, or drapes blocking heat registers or return air vents.

If you’ve gone through steps 1-4 above and your furnace still won’t come on, it’s time to call in the HVAC professionals. Newer furnaces have safety features such as sensors and a limit switch that will prevent your furnace from operating if they detect a safety issue. A technician can detect issues with the gas line or supply valve as well as other mechanical issues.

If you smell rotten eggs, you may have a gas leak. Leave the house and call your gas company. Once the danger has passed, an HVAC company can make recommendations for furnace repair or replacement.

Another issue that can result in your furnace not heating is an issue with the ignition system. Newer furnaces will have an electronic ignition system while older furnaces may have a pilot light. If the furnace is not igniting, you won’t have any heat.

With a newer furnace, you will need to call for furnace repair to have a technician open up the furnace to determine why the furnace ignitor is not working. They’ll check for error codes on the control board, and go from there. For an older furnace with a pilot light, you can try and reset the furnace and light the pilot light yourself. If the pilot light won’t stay lit, call in the professionals. 

If after ensuring the furnace is turned on and connected to the power supply, your thermostat is set to Heat, and you have a clean filter the furnace still won’t turn on, call a local HVAC company to come help.

HVAC professionals have the training and expertise to troubleshoot and find a solution for: 

• Complex electrical or gas issues
• Major mechanical failures
• Safety concerns
• Hard lockout

Some HVAC system maintenance you can do yourself, including:

• Replacing furnace filters regularly (every 30-90 days)
• Keeping return air vents clear
• Keeping supply registers clear

Your furnace needs good airflow to work properly. By changing the filters and keeping the vents and registers clear and unobstructed, you make it easier for your furnace to operate efficiently.

Schedule a furnace tuneup each fall. During the service visit, the HVAC technician should:

• Clean and lubricate furnace components
• Inspect and tighten electrical connections
• Test and calibrate the thermostat
• Test the furnace operation
• Make minor repairs or replace parts

Larger repairs will need to be scheduled separately. However, by scheduling yearly furnace maintenance, a technician can catch small problems before they become big ones. Consider signing up for an HVAC maintenance plan with your preferred HVAC company. They’ll contact you when it’s time for a maintenance call for your heating and cooling system.

Opt into Trane Diagnostics for peace of mind. Through the Trane Home App, you can give your dealer remote monitoring capabilities. Your Trane smart thermostat sends data in real-time to your dealer, alerting them to any issues, sometimes before you even realize there’s a problem. 

They can run furnace troubleshooting tests to pinpoint the problem. In some cases, they may be able to solve the problem remotely. In this situation, you would grant them one-time dealer remote access (DRA). 

If they need to schedule an on-site service call, the technician will arrive with the knowledge gained from remote access. This enables shorter service calls and ensures the technician has the proper replacement parts.

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.

Expert review by John Kim, Senior Product Manager, Furnaces

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