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Common Issues with the Furnace Limit Switch

The two functions of a furnace limit switch are turning the fan on and off during heating cycles and ensuring the furnace doesn’t overheat by shutting it down when its internal temperature is too high.

If you’ve been experiencing issues with your furnace limit switch and are looking to fix it, it’s important that you first understand what a limit switch is and how it operates. The furnace limit switch is a small but important device that’s used in forced-air furnaces powered by natural gas, liquefied petroleum, or heating oil. The furnace fan limit switch is engineered to monitor and maintain the interior temperature of the furnace. Once the furnace reaches a specific temperature, the limit switch turns the furnace on or off to keep the home at your desired temperature.

An additional function of the limit switch is that it has a maximum temperature control which disables the furnace before it overheats. Some limit switches also include a manual on switch that allows you to keep the fan on and create better airflow throughout your home.

It’s possible that your furnace may have two or even three limit switches that check the internal temperature at different parts of the furnace.

Why the furnace limit switch is important

The furnace limit switch is a safety feature that’s there to protect you and your family. The limit switch stops the furnace from overheating and thus damaging the internal mechanisms of the furnace and potentially other parts of your home. It also ensures that a comfortable environment is maintained throughout your home by controlling the home’s temperature and getting rid of any cold drafts.

Adjusting the limit switch

It’s possible to adjust the point at which the limit switch signals the burners to turn on and off, but we recommend that these adjustments are left to a trained HVAC professional. The factory settings for a standard furnace limit switch are 93 degrees celsius to turn off the blower, 54 degrees celsius to turn off the blower, and 38 degrees celsius to turn the blower back on.

Common problems with the furnace limit switch

Some common limit switch problems can be fixed yourself, while others require the expertise of a trained HVAC professional. A dirty sensor is one that can be fixed easily without any expertise. It’s common for old furnaces to start experiencing problems with the limit switch sensor as it has built up dirt and grime over the years which may prevent it from working correctly. This external build-up can be removed with a cloth or rag of any kind to get the sensor operating properly once again.

If your furnace is constantly turning on and off, this is likely the sign of a blower motor problem. When the blower motor is overheated it will cause the limit switch to trigger the furnace to shut off before the heating cycle is complete.

Faulty gas valves, circuits, and thermostats can also cause the limit switch to work improperly. We also recommend that you check to see if your furnace filter is clogged and in need of a replacement. A clogged filter can cause the furnace plenum to overheat and trigger the limit switch to stop the operation of your furnace.

We hope that you now have a better understanding of the furnace limit switch, its capabilities, and its common problems. If you have any further questions regarding the furnace limit switch or have any other HVAC concerns, don’t hesitate to contact us at any time. Our highly trained and experienced technicians are more than prepared to assist you with any of your HVAC problems. We provide efficient and quick furnace replacement done by our team of HVAC professionals. We offer a variety of furnace rental, purchasing, and financing options.

Give us a call at  1 (855) 998-2998 or fill out our online request form and we will be happy to assist you with your request.

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