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What can cause a furnace to stop working?

Sep 25, 2020

Cartoon of a CroppMetcalfe service technician with a toolbox standing next to a furnace in the home basement of a home.


Your furnace is subjected to a lot of pressure to keep your home warm and cozy, especially during the cold months of the year where that job becomes much more difficult. Due to the wear and tear caused by this workload, there are a variety of maintenance issues that could cause your furnace to stop working. Thankfully, a lot of these issues are relatively easy to resolve. However, some require an expert’s attention. 


Here are five reasons why you could be having a furnace malfunction:

What Can Cause a Furnace to Stop Working

1. Dirty Filters

Sometimes what can cause a furnace to stop working isn’t as complicated as you think. You might be surprised at how many issues a dirty filter can cause for your furnace. If you find that your furnace is not heating or blowing air normally, check your filter. 


Filters can trap dust and other debris, restricting the flow of air over time, causing your furnace to work harder to overcome the blockage which often leads to overheating. It can also prevent your unit from working properly and heating your home like you want it to. (Burnout due to overworking can also happen if your furnace is the wrong size for your home.)


You should replace your filter every three months at least. To resolve this issue, simply follow your owner’s manual to replace the old filter with a fresh, new filter.

2. Broken Thermostat

While you may think that the source of your furnace malfunction is the HVAC equipment itself, your issue actually could be due to your thermostat. To troubleshoot your thermostat, check the settings to ensure it’s on a heating mode and that it’s set to your desired temperature. Then, set it 5 degrees above your desired temperature and see if your furnace kicks on in response.


If there is no response, your thermostat could need new batteries or replacing. Try changing out the batteries and troubleshooting again, but if that doesn’t work, call your HVAC technician to inspect the issue.

3. The Furnace is Off

This might sound ridiculous, but before you call a technician to come inspect your furnace malfunction, try checking if it’s on. If you recently had repairs or maintenance done on your furnace, it’s possible the technician forgot to turn your unit back on. Look for a standard wall switch on or near your furnace, then check if it's at an “on” or “off” position. You can also double check your circuit breaker to be sure your furnace is getting power.

4. Water Leakage

If you notice a pool of water around your furnace while inspecting it, then you likely have some type of leak. Condensation leaks, humidifier leaks, plumbing leaks, and even a clogged internal drainage system could all lead to your furnace not working. Upon noticing the leak, it’s important to respond quickly to resolve it and prevent more serious problems from occurring.


Cut the power to your unit and call a professional to come inspect your furnace. Look for signs of an electrical issue, such as buzzing wires or sparks, before approaching the leaking water to mop it up. Do not touch the water if you see signs of electrical issues, as you could be at risk of electrocution. If possible, try to identify where the leak is coming from so you can inform the technician upon their arrival.

5. Broken Condensate Pump 

If you know your unit’s condensate pump is malfunctioning, shut your unit off at once. It is dangerous to continue operating your furnace if this part is broken or damaged. It may just need to be cleaned, but don’t worsen the issue by running your furnace with a malfunctioning condensate pump. 


Once your furnace is completely shut off, check the condensate pump to see if it’s become stuck in some way. Give it a good cleaning, then try running your furnace again. If the issue persists, call a technician to resolve the issue.

Schedule an HVAC Appointment with CroppMetcalfe

If none of these issues seem to be the problem for your furnace, or if none of the quick fixes resolve your furnace malfunction, it’s definitely time to call in a professional for help. Letting your furnace continue to run when it isn’t operating correctly could cause more severe issues and expensive repairs down the road. 


To get the issue addressed immediately, call CroppMetcalfe or contact us online today to schedule an appointment with one of our expert 5-Star Technicians!



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"I've been a CroppMetcalfe customer for 9 years and you have always provided outstanding service. I just had my semi-annual maintenance done, and I wanted to thank George for the truly outstanding service, professionalism, and excellent advice. He is definitely one of the best 5-Star Technicians I've had! Thank you CroppMetcalfe!"

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