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Why is My Heater Constantly Running?

Some heating equipment uses a fan to distribute warm air throughout a home. When the fan continuously blows, you might wonder, “Why won’t my heater turn off?” If it seems like your heating system is working overtime to keep your home’s temperature comfortable during the cool months of the year, a bit of troubleshooting is in order. 

Here are the most common situations where you might need to call an HVAC professional:

  • Incorrect thermostat temperature settings
  • Incorrect thermostat fan setting
  • Limit switch problems
  • Lack of weatherization
  • Dirty air filter

Common Problems & Solutions from Our Portland HVAC Experts.

Incorrect Thermostat Temperature Settings

When you set the thermostat to “Auto,” the heating equipment’s fan should only blow during the heating cycle. If the fan doesn’t stop running, check the thermostat’s settings. During the cooler months of the year, the thermostat should be set to “Heat” mode.

Once you confirm that it is in “Heat” mode, check the temperature settings. It should be warmer than the outside temperature, but not too warm. Try lowering the thermostat’s temperature setting so it’s cooler than the current room temperature. 

For example, if the thermostat is set to 75°F and the room temperature is 68°F, lower the thermostat to 65°F. Within a few minutes, the heating equipment should shut down, causing the fan to stop blowing.

If lowering the temperature causes the fan to stop running, the thermostat’s temperature was likely set too high. As a result, the heater worked hard to reach a higher temperature.

Incorrect Thermostat Fan Setting

In general, fans on thermostats have two settings: on and auto. If your thermostat’s fan setting is set to “On,” the fan will run all the time, even if the heating equipment isn’t warming your home. Other fan settings that may cause the device to constantly run include “Manual,” “Low,” “Medium,” and “High.”

The solution is to simply switch the fan setting to “Auto.”

Limit Switch Problems

If adjusting the thermostat’s temperature and fan settings doesn’t work, there might be a problem with the equipment’s limit switch. A limit switch’s job is to tell the blower when to turn off and on. In a furnace, you’ll find this switch under its hood.

After locating the fan limit switch, check if it’s set to “On” or “Manual Override.” On some models, the limit switch unit has a button you depress to set it to the “On” or “Manual Override” setting. These settings will cause the fan to continuously blow.

If the button is depressed, pull it out. This action will reset the limit switch to “Auto” so the fan only blows when the furnace heats your home. Check your heating equipment’s user manual to locate and identify the limit switch and familiarize yourself with its operation.

Lack of Weatherization

If your home isn’t weatherized sufficiently, cold air may enter your home while warm air escapes. This may occur around windows and exterior doors, electrical receptacles and light switches along exterior walls, recessed lighting units, cracks along exterior walls, attic, ventilation ducts, and chimneys.

Weatherizing your home and improving its insulation will help your heating system run more efficiently when it has the correct settings.

Why isn’t My Heater Working? When to Call a Portland HVAC Professional.When to call AAA Heating and Cooling

  • Your heating equipment continuously runs but never reaches the set temperature, even when all the settings are correct.
  • The fan continues to blow after you reset the limit switch; wires may be misconnected or shorted.
  • You can’t depress or pull out the limit switch button.

If you can’t remedy a heater that is always running on your own, it’s best to call an HVAC professional like AAA Heating and Cooling. Hiring a specialist will help solve your heating problems faster and prevent voiding an active warranty by accident. 

Get in touch with AAA Heating and Cooling today about your heating questions or concerns.