Why Won't My Heater Turn Off? | Furnace Repair
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How Do You Fix a Gas Furnace That Won’t Turn Off?

A home's energy-efficient furnace in a basement

Ideally, your furnace should turn on when the thermostat senses that it’s too cool in your home and turn off when the temperature reaches the thermostat’s set point. If it’s not cycling on and off but running constantly instead, there are a few possible causes of this problem.

Why Is It Bad for Your Gas Furnace to Always Be On?

When your gas furnace runs continuously without breaks, it will substantially increase your energy bills and could also damage the furnace and shorten its lifespan.

Components like the blower motor or induction motor could overheat, damaging the motor windings and bearings, or the heat exchanger could overheat and crack. These are expensive repairs, so it’s important to address the problem quickly to avoid further system damage.

What to Do When Your Furnace Won’t Turn Off

Several issues can stop a furnace from cycling on and off properly. Here are some of the most common problems to check for and their possible solutions:

  • Incorrect temperature settings: Make sure your thermostat is set correctly. If the set point was raised inadvertently, the furnace will keep running until that temperature is reached, even if it’s set to 90 degrees. Change the thermostat to a lower setting than the current room temperature so the furnace turns off.
  • Wrong fan setting: Normally, the furnace’s fan should turn on shortly after the furnace does and shut off soon after the furnace turns off. If the the fan is set to “On” instead of “Auto,” it will run constantly, even though the furnace is off. This can make it seem like the furnace is running, however. Set the fan back to “Auto” so it cycles normally.
  • Low thermostat batteries: A digital or programmable thermostat is typically powered by batteries, and if these are low or dead, the furnace may not cycle properly. Replace the batteries with a fresh set at least twice a year.
  • Faulty fan limiter: The fan limiter controls the cycling of the blower fan, delaying it slightly when the furnace turns on to avoid blowing cool air through your home and turning the burners off to protect the heat exchanger if the furnace gets too hot. If the fan limiter is faulty, it may allow the fan to run constantly. To fix the problem, have it replaced by a professional HVAC technician.
  • Dirty air filter: If your furnace filter is clogged with dust and debris, it can interfere with airflow through the ducts and the thermostat’s temperature readings, stopping the furnace from cycling properly. To fix the problem, improve your air quality, and keep your furnace running as efficiently as possible, check the air filter every month and replace it as needed.
  • Leaking air ducts: If your furnace is running but much of the hot air is escaping through leaks in the ductwork, the house may never reach the thermostat’s set point, and the furnace will keep running. Have a professional inspect and repair the ductwork.

Schedule Furnace Service With Andreas Plumbing, Heating & Air Conditioning

If your furnace still doesn’t shut off, talk to our home heating experts at Andreas Plumbing, Heating & Air Conditioning.

We offer in-depth diagnostic services and furnace repairs to quickly resolve any problems you may have with your furnace, as well as complete furnace maintenance that can prevent problems while keeping your heating costs as low as possible and making your furnace last longer.

When you want to make sure your furnace is always performing at its best, our Service Partner Plan is a great value. It offers all your annual HVAC maintenance, excellent benefits like priority service, no emergency service fees, and a 10% discount on all our HVAC services.

Our company serves homeowners throughout Carbon County, Lehigh County, and Monroe County, as well as select areas of Northampton and Schuylkill counties. We’re a fourth-generation, family-owned HVAC company offering top-rated customer service and quality that reflects our commitment to honesty, integrity, and hard work.

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