Reasons Your Furnace is Still Running After Reaching the Set Temperature


During the cold winter months, we rely on our furnaces to keep our homes warm and comfortable. However, there may be times when we notice that our furnace continues to run even after it has reached the set temperature. This can be a cause for concern, as it may indicate that there is an underlying issue with your heating system. In this blog post, we will explore some common reasons why your furnace may still be running after reaching the set temperature.

1. Incorrect Thermostat Settings:

One of the most common reasons why your furnace is still running could be due to incorrect thermostat settings. Ensure that your thermostat is set to the desired temperature and that it is not set to the “continuous” or “fan” mode. In these modes, the fan or heating system will continue to run regardless of the actual temperature in your home. Double-checking your thermostat settings can help resolve this issue.

2. Dirty Air Filters:

Another common culprit for a furnace that keeps running is dirty air filters. Over time, air filters can become clogged with dust, debris, and other particles, inhibiting proper airflow. When the airflow is restricted, it can take longer for your furnace to reach the set temperature, causing it to continue running. Regularly changing or cleaning your air filters can help prevent this from happening and also improve the overall efficiency of your furnace.

3. Thermostat Placement:

The placement of your thermostat can also contribute to your furnace running longer than necessary. If your thermostat is located near a window, vent, or any other source of drafts, it may receive inaccurate temperature readings. This can trick your furnace into thinking that the temperature has not yet reached the desired level, causing it to keep running. Consider relocating your thermostat to a more central area in your home to avoid such issues.

4. Leaky Ductwork:

Leaky ductwork can lead to warm air escaping before it reaches the desired areas of your home. When this happens, your furnace will continue to run in an attempt to compensate for the lost heat. Sealing any leaks in your ductwork can help resolve this issue and improve the efficiency of your furnace.

5. Malfunctioning Thermostat:

If you have ruled out the other common causes and your furnace still runs continuously, it is possible that your thermostat is malfunctioning. A faulty thermostat may not accurately measure the temperature or send the correct signals to your heating system, causing it to run longer than necessary. If you suspect a malfunctioning thermostat, it is advisable to contact a professional HVAC technician to diagnose and replace the thermostat if needed.

6. Oversized Furnace:

An improperly sized furnace can also be a reason why it continues to run after reaching the set temperature. A furnace that is too large for your home will heat it quickly, but it may shut off before the whole space reaches the desired temperature. As a result, the furnace will turn back on soon after, leading to constant cycling. If you suspect that your furnace is oversized, consult a professional to evaluate your heating needs and recommend the appropriate furnace size.


There can be various reasons why your furnace is still running after reaching the set temperature. Checking your thermostat settings, regularly changing air filters, ensuring the proper placement of the thermostat, sealing leaky ductwork, and addressing any thermostat malfunctions are all important steps in troubleshooting this issue. It is also worth considering the size of your furnace to ensure it is appropriate for your home’s heating needs. If you are unsure or unable to identify and address the problem, it is always best to contact a professional HVAC technician to diagnose and resolve the issue to ensure the optimal performance of your furnace.

Need HVAC Services in St. Louis, MO?

Keep cool or stay warm with Ashley Brothers Heating & Cooling. Since 1999, Ashley Brothers have been providing residential and commercial services to the St. Louis and Jefferson County area. We specialize in the installation of new equipment, heating and cooling repair, and furnace cleaning. Craftsmanship is important, equipment choice is too. We work with only top brands like Amana, Goodman, York, and McLain. It is understandable that replacing or upgrading your equipment can be daunting. Ask us about financing. We repair all heating and cooling equipment brands. Heating and cooling repairs can happen at random, take advantage of our 24-hour emergency service. Call us today about your concerns.