Why Won't Your Furnace Turn Off?

Front view of falling snow with home during rare storm in Pacific Northwest of United States

When the weather is chilly outside, having a furnace that won’t turn off might not seem like a problem at first, but left unchecked, struggling heating systems can cause all kinds of problems. When furnaces don’t turn off when your thermostat directs them to, your system may be wasting loads of energy, increasing the cost of your heating bills. Over time, heating that doesn’t turn off can also damage delicate internal components, such as sensors and heat exchangers.

Fortunately, you don’t have to let problems with your furnace interrupt your home comfort. Our technicians here at Jarboe’s Plumbing, Heating & Cooling are committed to spotting and fixing issues within furnaces to make your home more comfortable. Whether you are having a problem with your fan, blower, thermostat, or electrical circuit, our NATE-certified technicians can make things right. Here are a few reasons your furnace may not be switching off, and what to do about it.

Why Furnaces Keep Running and Won’t Turn Off

Furnaces that aren’t shutting off regardless of the room temperature can signal issues within your system. Sometimes these problems are complex, while other times they can be fixed in a few minutes by a savvy homeowner. Here are a few reasons your system may not be shutting down.

1. Thermostat Set Improperly

Anytime your thermostat is set too high, it may not trigger your furnace to turn off. Before you assume your heating system is broken, check the settings on your thermostat to see if someone may have turned up the room temperature in your home without letting you know. Here are a few other things to try before advancing through more complex troubleshooting.

  1. Temperature Setting: Is the room temperature set higher or lower than you might like? See what the system is set at, and then adjust the temperature up or down according to what you might like.
  2. Manual Turn Off: Try turning off the furnace by manually lowering the room temperature. Dropping the temperature a few degrees lower than the current setting should trigger the furnace to turn off. If it doesn’t, try turning the system from “HEAT” to “OFF.” Systems that need to be manually switched off may require a professional tune-up, since there could be problems with the thermostat wiring or the blower motor.

2.  Wrong Fan Settings

Furnaces are designed to run through heating cycles when the thermostat senses that the ambient temperature has dropped too much. However, sometimes your furnace may operate even when it isn’t heating, especially if your blower fan is on the wrong setting. Blower fans can run independently of your furnace system, which is helpful if you need to temporarily increase airflow throughout your home, such as drying carpet that was recently cleaned. However, doing so can drive up energy costs. Here are a few things to check when it comes to your fan settings.

  1. On your thermostat, look for the “ON” and “AUTO” settings. On a manual thermostat, this may be a physical toggle switch. On a digital thermostat, look for “Fan Settings.”
  2. Check your thermostat to see if the unit is set to “AUTO” instead of “ON.” When the “AUTO” setting is on, the furnace will run regardless of whether it is heating your home or not, which can waste energy.

3. Clogged Air Filter

Dirty air filters can hamper airflow, while simultaneously allowing dust and dirt to circulate through your home. If the filters become dirty, dust can also build up within your furnace, which can harm sensors and components. To remedy this problem, replace the air filter.

  1. Open the filter compartment of your furnace and remove the old filter.
  2. Place a new filter with matching dimensions in the compartment. Make sure the arrow on the side of the filter is situated in the same direction airflow would travel through the filter.
  3. Throw away the old filter and replace the compartment door.

If your HVAC system uses a washable, reusable filter, vacuum the filter with the upholstery tool on your vacuum, and then rinse it with water. Lay the filter out on a clean, dry towel to let it dry completely before reinsertion.

4. Malfunctioning Thermostat

Your thermostat is responsible for gauging the ambient air temperature inside your home, and carefully triggering the furnace to turn on or off. Unfortunately, if thermostats develop problems, they may miscommunicate with your system, causing your furnace to run more often than it should. Loose wiring is one problem that causes malfunctioning thermostats. Here are a few tips to check your thermostat and tighten the wiring.

  1. Shut down the power to your furnace or heat pump by using the circuit breaker.
  2. Take the thermostat cover off to access the wiring panel.
  3. Check to see if any of the wiring connections are loose. Tighten down loose connections with a screwdriver.
  4. Put the thermostat cover back on and restore power to your system.

If tightening the electrical connections of your device doesn’t seem to work, a professional may be able to repair the problem. However, in many instances, the thermostat may need to be replaced. Sensors or switches within the thermostat can break. Professional HVAC technicians can talk with you about your thermostat options.

When to Call in a Pro

If the troubleshooting steps above didn’t help your furnace to run like it should, don’t despair. Deeper issues within your furnace like failed limit switches or compressor contact can cause the phenomenon, but our team can spot and resolve problems quickly. Our thorough team can come out anytime, day or night to fix your furnace, so give us a call.

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