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Common Furnace Problems and How to Fix Them

December 30, 2025
Common Furnace Problems and How to Fix Them

Being knowledgeable about the most common furnace issues that may come up during the winter season and how to fix them will help you keep your system running efficiently and help lower your risk of having to do costly repairs down the line. Although there are many different things that can go wrong with a furnace, below we explain common furnace problems and how to fix them.

Dirty Furnace Filter

A dirty air filter is one of the main causes for breakdowns in both air conditioners and furnaces. Dirty air filters can become clogged with dirt and dust which can impede air flow and cause your furnace to work much harder than usual. Furthermore, a dirty air filter can also cause a furnace to frequently turn on and off. This can not only cause your home to feel uncomfortable, but increases your energy consumption and the likelihood of a breakdown. Be sure to check and/or change your air filter periodically, especially during the heating season to lower the risk of this issue.

Thermostat Malfunctioning

If your furnace is not heating up at all check your thermostat and make sure the setting is set to heat. Next check the batteries and be sure to replace them if they need to be replaced so the thermostat has enough power to activate the furnace. Lastly, make sure thermostat is in a place away from any heat sources to avoid false readings. If you have checked settings and replaced batteries and your furnace is still not blowing warm air and/or your thermostat needs to be relocated, please contact a professional.

Furnace Switch and Electrical Panel

If you have checked air filter and thermostat and both are fine, power could be the problem. Check that the furnace switch is turned to on, someone may have accidentally turned it off. If that does not work, then check the electrical panel. To reset breaker, flip the switch all the way to the off position before turning it back on. If the power to furnace is still out or breaker continues to trip it is best to let a professional diagnose the issue. If there are any signs of electrical damage or you don’t feel comfortable it is best to contact a professional.

Pilot Light and Ignition System Issues

If your furnace is not turning on at all, one common reason is that you are having issues with the combustion system. A gas furnace depends on a pilot and ignition system to operate. These systems are prone to dirt and soot buildup overtime especially if the furnace is frequently used and not maintained properly. When these components become dirty, they affect the ability of your furnace working and heating your home properly.

The most common sign of a dirty pilot and ignition system is the absence of a pilot light or one that burns yellow or orange and rumbling noises when your furnace is turned on. If you have a system with a pilot light that has blown out, you can very carefully relight the pilot on your own after consulting the owner's manual. If the pilot continues to blow out, you can contact us for service to diagnose the issue. Remember that if at any time you smell gas it is important to evacuate the home and call your local gas company. If you have a modern gas furnace without a pilot light, remember that safety switches and computer boards can also fail.

If you believe there may be a problem with the combustion assembly, it is important to call for professional service.

Continuously Running Blower Motor

If the furnace blower is continuously running it may mean that there is a problem with the limit switch. First, you will want to set your thermostat to a temperature that’s lower than the current room temperature and make sure the fan is set to Auto. If the fan continues to run, check the limit switch and make sure it is set to Auto and not manual override which would keep it constantly running. If the limit switch was already set to Auto (not pushed in), then you most likely either have a problem with your thermostat wiring or the fan limit switch. Unfortunately, both issues will need to be fixed by a professional.

Call LA Construction Heating & Air Conditioning at (818) 341-3406

When in doubt about what may be causing your furnace to malfunction, contact LA Construction Heating & Air Conditioning at (818) 341-3406 or online. Remember to always let professionals handle any issues that may arise due to mechanical wear and tear. To learn more about services we offer, please visit our homepage.

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