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What Causes a Furnace to Stop Working?


Are you wondering why your furnace just suddenly stopped working? Did it just happen abruptly with no warning? If that’s the case, then maybe we can help point you in the right direction. In this month’s blog post, we’ll be talking about the signs of a broken furnace, reasons why a furnace may stop working, and what to do next if you can’t fix it. If this blog post helps you out, feel free to leave a comment below! You can also leave a comment if you have any additional questions. Now, let’s get into the blog post.

Signs of a Broken Furnace

There are plenty of signs that your furnace isn’t working with the most obvious one being that it won’t turn on. However, that is not always the case. There are signs of a broken furnace that are not always so black and white. In this section, we’ll be covering five signs of a broken furnace. 

  • Excessive Dust Buildup

If you notice excessive dust buildup in your home then your furnace may not be working properly. Excessive dust buildup can be caused by your furnace not being able to circulate air. You should check your furnace’s filter and see if that is the cause of your problem. If you haven’t replaced your furnace in a while, it is likely that a clogged filter is the reason why your filter is not working. 

A Man Troubleshooting a Furnace
  • No Hot Air

Another sign of a broken furnace is when there is no hot air blowing out of it. There might also be cold air blowing out of your furnace. You should first check on your filter and see if it is dirty. If it is, replace it and see if there is a change. If there is a change, the issue might not have been with your furnace but specifically with your filter. A clogged filter prevents proper airflow. A way to make sure you don’t have a clogged filter is to replace your filter frequently as recommended. Depending on the size of your filter depends on how often you should replace it. A rule of thumb though is the thicker the filter is, the longer you can go without replacing it. 

  • Strange Odors Coming from Furnace

If you smell something such as rotten eggs or burning dust from your furnace, check it out right away. If you smell rotten eggs in your house for any reason at all, you likely have a gas leak.  Evacuate your house and call the fire department. If you smell burning dust from your furnace, check your furnace filter. If you haven’t used your furnace in a while then it is likely just the cause of dust buildup from lack of use. The odor should clear out after a while and not cause any damage to you or your furnace in the process. 

  • Carbon Monoxide Poisoning

Carbon monoxide poisoning is a silent killer that can happen because of a gas leak. In oil and gas furnaces, carbon monoxide is produced. The carbon monoxide is usually contained inside your furnace, but sometimes a leak happens. Your furnace will not be working properly if there is a gas leak and you and your family will be at risk. Some signs of carbon monoxide poisoning are dizziness, headaches, vomiting, confusion, and shortness of breath. If you suspect you have carbon monoxide poisoning you should call poison control immediately and evacuate your house. Carbon monoxide is an odorless gas and cannot be detected unless you have a carbon monoxide detector. A carbon monoxide detector measures the amount of carbon monoxide in the air and warns you if it gets too high.

Carbon Monoxide Detector

Explanations Why Your Furnace Stopped Working

There are different reasons why your furnace may have stopped working. If you can narrow them down, you can figure out how to fix it and get it back to optimal condition again. 

  • Old Age

Your furnace may just have stopped working due to old age. A furnace usually lasts between 15-20 years depending on the amount of care it was given, its type, and model. Old age comes for all furnaces eventually. You can increase your furnace’s lifespan by taking care of it. In our blog post, “How to Take Care of Your Furnace,” we highlight some tips and tricks for taking care of your furnace. 

  • Your Home Circuit Breaker Needs to Be Reset

Your home circuit breaker may be the issue with your furnace. All furnaces, even gas furnaces, use electricity. If your furnace isn’t working, try resetting your home circuit breaker. To safely reset your home circuit breaker, turn off all your lights and unplug everything. Then reset the main breaker on your circuit breaker by turning it off. Wait a little bit and turn it on again and see if that helps. If you want to specifically only reset the circuit breaker used for your appliances, then you need to reset the double-pole breakers. You can read more about resetting your home circuit here.

Circuit Breaker
  • Your Furnace is Clogged

As mentioned in the above section regarding a furnace that doesn’t produce heat, your furnace might be clogged because of your filter. If your filter hasn’t been changed in a while, particles will get stuck in it and prevent air from passing through. The more buildup in your furnace’s filter, the worse it is going to be able to do its job. In order for your furnace to keep working, you have to change your filter as recommended. 

  • Your Thermostat Malfunctioned

The reason your furnace may not be working is because of your thermostat. Some issues that are correlated with furnaces not working and thermostat malfunctioning are furnaces producing too much heat and not enough heat. A few ways you can figure out if your thermostat is the issue is to replace the battery if it is electric. If you notice that your furnace is working right after you replace your thermostat’s battery, the issue was with your thermostat and not your furnace. 

Person Changing Furnace Filter

What You Can Do

If you have tried everything and still can’t figure out why your furnace isn’t working, you can call an HVAC company and talk to them about the issue. Sometimes your furnace can’t be fixed with just a simple solution. You should talk to the HVAC technician and tell them what you have already tried doing. This can help them to narrow down the issue. We do not recommend you try to  repair your furnace yourself unless you are an HVAC technician. A lot of HVAC companies will not want to touch furnaces that have been clearly altered by homeowners or other companies. HVAC companies can potentially be held responsible if anything goes wrong after a homeowner or another company tries to fix a furnace. Save yourself the heartache. Make sure you research an HVAC company before letting them into your home and leave more complicated fixes to the professionals. 


We hope we were able to help and answer your question about why a furnace may not be working. Sometimes it can be easily solved by routine maintenance and just resetting a thing or two. Sometimes it can’t be, however, it’s good to know what to do in the future if a problem arises again. If you need to have your furnace repaired and live in Jefferson County and any surrounding areas, contact us! We would be happy to assist you in all of your HVAC needs. 

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