When the outside temperatures plummet, your home can be a warm retreat. You can turn on your furnace and the indoor air will heat up. This system is reliable and it usually works like a charm, but what happens when it doesn’t? What if you turn your furnace on and no warm air comes rushing out of your vents? This is actually a common issue. A lot of consumers get frustrated at times like these, especially when the outside temperature drops fast. However, keeping a level head will allow you to assess the possible causes one at a time.

Why Am I Not Getting Any Heat When My Furnace Is On?

The fact that your furnace is still turning on is a good thing. This means that the power supply is in good working order, but something else within the system is keeping everything from working as it should. The issue may lie with a simple oversight that requires just a few quick tweaks to get everything back in order. This is usually the case and thus, there’s no need to panic. If the problem proves to be more complex than you’re capable of handling on your own, you can pass it on to a licensed HVAC technician.

This article will cover the most common reasons why your furnace isn’t generating heat even though it’s turned on. These include not having the right setting at the thermostat, problems with airflow, insufficient fuel, and issues with the furnace ignition.

We will talk about how things can go wrong in each of these areas. We will also show you how to use basic troubleshooting measures to set things aright. These are simple steps that every homeowner can take on their own. With luck, your furnace will immediately kick back into action and the whole trouble will be behind you. However, if your furnace remains responsive after troubleshooting, don’t try to take on more involved repair issues. Call an HVAC company to get professional help. Learn what you can from this experience, and take steps to prevent the problem from occurring again.

Problems at the Thermostat

image of homeowner adjusting programmable thermostat

Furnaces are built to perform as they’re instructed. If your intentions and what you instruct your furnace to do don’t match, you’re going to get unexpected results. The thermostat is the brain or control center of your entire home heating system and thus, you have to be sure to input the right information. For instance, you might want the heater to generate warm air but you haven’t yet set the thermostat to do trigger heat production. In this case, there really isn’t anything wrong with your furnace. You just need to change the settings to reflect your heating goals. It might be that the thermostat is set at COOL and you have to toggle it over to HEAT. It could be that someone else in the home has adjusted the thermostat while you were gone or when you weren’t looking. Never simply assume that the thermostat is correct. Instead, take the time to check the basics.

Check the fan settings as well. A lot of homeowners think that if the fan is moving the furnace should be generating and distributing heat, but this isn’t always the case. If it is in the ON position, it will run all of the time, even when it isn’t in the middle of a heating cycle. It is far better to set the fan to AUTO instead so that it will only spin during heating cycles. This will ensure that only heated air is being forced through the vents. You also have the option of setting your thermostat higher. Try raising the thermostat by just five to 10 degrees and you’ll likely feel a noticeable difference. However, if you do these things and only cold air is being produced, you should call the professionals in.

Problems With Airflow

For the furnace to function properly, air must be able to travel freely through this system. If there is an issue with the airflow, then heat won’t be able to travel from the source into individual rooms. One reason why your furnace might not have heat coming out is an obstruction that’s blocking the flow of air. Following are several common culprits:

The Air Filter Is Dirty

image of a dirty furnace filter

Air filters are critical components for blocking pollen, pet dander, dirt, dust, and other forms of airborne debris. These filters keep the ducts and the furnace interior from getting dirty, but they accumulate a lot of gunk in the process. Over time, their surfaces are covered in a thick layer of dirt that keeps air from freely moving through them.

Homeowners should check their air filters monthly and should replace these components as needed. While many can follow the recommended filter replacement schedule from your furnace manufacturer, there are various factors that will determine the best time for an HVAC filter replacement. Some may have to change their filter out more often, especially if the home has a lot of pets or is located in an especially dusty neighborhood.

The Vents Are Closed

closed HVAC vent

Your issue might be as simple as having a few closed vents. Make sure that the louvers are open throughout your home and adjust these necessary. They may get stuck so it’s always a good idea to remove vent covers and clean them periodically. If these covers are jammed, consider replacing them. You can additionally make sure that nothing is blocking the air registers or vents. It may be that someone has moved your furnishings to block a vent off. Putting things back where they were will ensure good airflow.

Fallen Debris & Other Obstructions

There may be items that have fallen down into the heater vents. Remove the vent covers and use a flashlight to see all that’s inside. If there are any objects that you can reach in and take them out right away. You can use a pair of gloves for safety if you aren’t sure what you’re retrieving. For items that are difficult to reach, try using a long stick or a wire.

Furnace Ignition & Fuel Problems

gas furnace flame

Furnaces that turn on but fail to produce heat may have low fuel. Without a source of energy, your furnace isn’t going to be able to accomplish much. If you rely on gas, check to ensure that the gas valve is in the open position. You may even want to contact the gas company to verify that your service hasn’t been interrupted. If it has, then find out when service will be restored.

If you are using heating oil or propane, see how much fuel you have left. Schedule delivery service if you need it. This is a problem that you can keep from recurring by simply monitoring your fuel levels and being mindful of how much fuel you’re using on a regular basis. There are even monitoring devices for keeping track of fuel levels. Last, you can have a heating oil company handle fuel level monitoring so that they can schedule timely refills for you.

After you are sure that you have plenty of fuel, consider the ignition system as being the source of the problem. The ignition system has the job of starting fuel combustion. If it isn’t working as it should, your furnace won’t be able to generate enough heat. For older models, make sure that the pilot light is lit. If it is, follow the instructions in your manual for relighting your pilot light. For a newer furnace model, check the ignition switch in your heater’s electronic ignition system. If there is dirt on the metal strip, carefully clean this and then retest the ignition.


When your furnace turns on but won’t heat up, this can definitely cause some confusion. This article has hopefully shed some light on the issue. The next time you face this problem, you’ll know the best troubleshooting measures to take. In the event that the above-mentioned tips don’t work, you can schedule professional service instead. Licensed HVAC technicians have the skills, tools, and training for tackling a variety of complex problems. They can quickly and accurately diagnose the underlying cause of this issue and apply the best possible solutions.