Furnace Not Igniting? Common Causes and Fixes

Furnace Troubleshooting Can Often Get Your System Working Again

Though a furnace can stop working at any time in the year, most homeowners don’t discover issues until they turn it on during the fall after sitting idle for months. If your furnace fails to ignite, there are a few simple checks you can do yourself to get your system up and running again. However, you should call a professional HVAC technician to make major repairs. You don’t want to get into the middle of repairs and realize you are in over your head. Try these troubleshooting tips before calling in the professionals.

Furnace Not Igniting Because of Incorrect Thermostat Setting

Many homeowners forget they need to change their thermostat setting back to “heat” or “heating,” typically sometime in the fall when the weather cools. An accidental change or power outage could also mean you need to reset your thermostat to your preferred setting. Before we get into more difficult fixes, check your thermostat.

Make sure the thermostat is set to heating and that the temperature is set high enough to actually turn the furnace on. It may be set at too low of a temperature to activate the furnace.

Newer smart or programmable thermostats may alert you to any potential issues with the unit. There may be an error code, or it might even tell you what is specifically wrong with your furnace.

Furnace Won’t Ignite Because of a Dirty Air Filter

Furnaces need an adequate amount of air to be able to operate smoothly. Restricted airflow can lead to a host of issues including increased energy consumption, uneven heating, and system damage.

If you forget to regularly change your air filter, it can become clogged and dirty, potentially causing your furnace not to ignite. To change your air filter, open up the metal grate that houses the filter and remove it. Does the filter look physically dirty or caked in dust? If so, it is time to change your air filter.

Get into the habit of changing your air filter every 1-3 months. If you have any pets or if you live in an area with a lot of pollen or pollutants, you may need to change it more often. Some air filter companies advertise a longer lifespan for their filters. However, it’s more important to rely on your home’s environment for filter changing than anything else. A good rule of thumb is to check your air filters once a month.

If improper airflow has tripped your furnace to power off, you’ll need to reset the power before it works again. Turn the breaker off then on again, or unplug and reconnect the furnace itself. Bottom line: keep your air filter clean. It will improve the performance of both your furnace and AC system. 

Furnace Not Igniting Burners Due to Tripped Circuit Breaker or Blown Fuse

It’s possible a tripped circuit breaker or blown fuse may be the underlying reason your furnace is not igniting properly. Though this may seem like too simple a problem, rule it out before proceeding.

Go to your electric panel and see if any of the circuit breakers have been tripped. If so, turn them back on. If it immediately trips again, you may have a short somewhere in your system. Do not try to turn it on again. Contact an HVAC technician.

If you have an older home with a fuse panel, you will want to turn the power off to your entire house. To do this, pull out the main fuse block. For extra safety, an amp meter should also be used to verify that power is truly off.

Next, remove the fuse that corresponds with your furnace. If it looks black or cloudy, or there is a visible gap between the main center wire, then the fuse has blown. Refer to the amperage rating at the top and replace it with a fuse of the same number. Do not try to use a lower or higher fuse as this will cause the fuse to blow out once again and could damage your furnace even further.

Gas Furnace Will Not Ignite Because of a Faulty Gas Line

A faulty gas line could be the reason your gas furnace is not lighting. First, check and make sure that your gas is turned on. Your shut-off valve should be outside and will resemble a rubberized strip of metal about five inches long. If it is perpendicular to the gas pipe, then it is turned off. If it is parallel with the gas pipe, it should be on.

However, if you have any other gas appliances in your house, such as a gas stove, you can simply check to see if it is working. If you are able to light a burner, for example, or a gas fireplace, then your gas line is not turned off.

Though naturally odorless, natural gas has an odorizer called mercaptan added to it to give it a rotten egg smell. If you smell something peculiar and suspect you may have a gas leak, exit your house and call 911 immediately.

Oil Furnace Won’t Ignite Because It’s Turned Off

Both oil furnaces and gas furnaces have a physical power button. If the furnace is located in a space that people frequent, it is possible the main power switch has been turned off. Locate it and make sure it is turned on. If it turns on for a moment and then immediately turns back off, there is an internal issue, and you should contact an HVAC technician before investigating further.

Furnace Pilot Light or Electronic Ignition Isn’t Working

If you have an older gas furnace, your system uses a pilot light to ignite the burners. You should see it inside of your furnace just above the burners. If it is lit, it is not the cause of your problems. If not, you can use a small match to light it back up. However, if this fails to turn your furnace on, then your issues are more substantial, and you should call a professional.

If you have a newer furnace, you have what is called an electronic furnace ignition. Also located above the burners, an electronic furnace ignition heats up as an electric current runs through it. If it is running, it should glow and produce a popping sound.

If you hear a lot of popping sounds but the system is not igniting, this usually means that it is dirty. Turn off the system, unscrew it from the furnace frame and clean it gently with a small cloth. Once clean, carefully reinstall it and turn the power back on to your furnace. Note: You may need to turn the temperature up to get the furnace to engage.

Gas or Oil Furnace Is Not Igniting Because of Dirty Burners

Dirt or grime on the burners themselves can restrict airflow and prevent the burners from lighting. If the burners look dirty, you can try cleaning them to get them to ignite.

To clean them, turn off power to the furnace by flipping its circuit breaker to the off position. Next, remove the burners using a drill and clean them with a hard-wired brush. Remove as much as possible from all sides of the burners and then spray the entire unit with a can of compressed air. Once the burners are clean, reattach them to the frame and turn the power back on. Most homeowners may prefer contacting a professional to clean dirty burners to ensure the task is completed safely and correctly.

Furnace Maintenance Tips

To ensure your furnace runs smoothly when you need it to, follow these maintenance steps throughout the year.

• Routinely clean/replace air filters
• Have your furnace and thermostat inspected by an HVAC technician once a year

Should I Repair or Replace My Furnace?

A professional HVAC technician will tell you if it is time to replace your furnace system. Some tell-tale signs, however, include:

• Increased energy bills. This suggests your furnace is not running as efficiently as it once did
• Increased dust and particles in the air while the furnace is running
• Excessively dry air in the winter
• Furnace frequently requires repairs
• Furnace frame is cracked or rusted
• Rooms are not heating evenly
• Furnace is older than 20 years