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Education4 Reasons Why Your Furnace is Running Constantly

4 Reasons Why Your Furnace is Running Constantly

An ongoing operation of your furnace can create problems with ductwork, overwork of its blower motor, and electrical issues like corroded wires that require professional expertise to rectify. When working with electricity, seeking assistance from qualified personnel is always wise.


Before calling in a professional, there may be several simple troubleshooting steps that may help.

Before reaching out to experts like River Valley Heating Repair for electrical or blower motor issues, trying out a few troubleshooting steps might just save the day!

1. Thermostat issues

If your furnace runs constantly or turns on and off frequently (short cycling), this can cause extensive damage. Not only could it wear out more quickly than intended, but it may even overheat, endangering all electrical components of your home.

One simple solution is to ensure the thermostat is set appropriately. This can be accomplished by switching it from “on” to “auto”, as on causes the fan to operate continuously; auto only activates its fan during heating cycles.

Your thermostat could also be compromised by dust accumulation that restricts airflow and requires your furnace to work harder in heating your home. Try cleaning it by unplugging and gently brushing away any dust accumulation from its housing while changing batteries annually to ensure smooth operation of the device.

2. Dirty air filter

One of the primary factors contributing to a furnace running is a clogged air filter. Air filters are created to filter out dust, pet hair, and other forms of debris before entering your heating system, but when they become clogged too often, they hinder airflow, leading to overheating in your heat exchanger and forcing you to operate your furnace constantly.

At times, your furnace’s blower fan may keep running even after it has been turned off by your thermostat, leading to heat being dispersed throughout your home and possibly leading to furnace shut-offs that continue. Replacing air filters at least every month during winter should help.

Check that your air vents are clear of furniture or other objects in the room; leaky ductwork may restrict warm air from flowing freely and force your system to work harder than necessary in heating your home. In such instances, professional advice should be sought so as to make sure your furnace is sized accordingly.

3. Fan limit switch

If your furnace is running continuously and you have checked the air filter, and it still does not stop, it could be that the fan limit switch has been manually switched to “on.” Typically, this switch located on older thermostats regulates when and how often a fan turns on and off; typically, only during heating cycles should the fan run continuously.

Fan limit switches for furnaces are small metal boxes placed above or next to your furnace and typically feature an extended temperature sensor that reaches into your plenum – the main branch of ductwork in your home that connects every room – as a safety mechanism to keep overheating at bay. They must always function effectively to safeguard family safety.

To switch it back into AUTO mode and get it to turn on/off automatically with your furnace operation and shut off when the desired temperature has been achieved, simply pull out the white knob on the fan limit switch and push in (or follow the instructions on the manual). It should now turn on/off as desired!

4. Loose or damaged wiring

Loose or damaged wiring may be another issue that keeps your furnace running unnecessarily and is best handled by professionals due to improperly connected wires leading to short circuits.

To repair loose or damaged wiring, take steps such as removing old tape, cleaning up connections and using wire nuts or approved connectors on each end. Also, stripping off approximately 3/4″ of insulation on both ends will make reconnection much simpler and faster.


Heat is essential, but too much can be a wasteful expense. If your heating system continues to operate long after its target thermostat temperature has been reached, this wasteful energy consumption costs both energy and money each billing cycle.

Contact a professional to get your furnace working properly again.

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