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Though a furnace that fails to turn on is a major problem that no one wants to deal with on a cold day, a continuously running furnace is also problematic. For instance, if your furnace fan won’t turn off, your heating system is likely experiencing a problem that will affect the furnace’s performance and your indoor comfort.
For trusted furnace repair in Columbia, PA, residents turn to Topline Heating & Air. Here, our HVAC technicians share reasons why a furnace fan constantly runs and what you could do about it.
1. Incorrect Thermostat Settings
One of the primary problems to check for when your furnace fan won’t turn off is an incorrect thermostat adjustment. If your thermostat settings have the fan on “auto” instead of “on,” the fan will turn off with the furnace as soon as the indoor temperature reaches what’s on the thermostat. Unfortunately, leaving the fan on the “on” setting will keep the equipment running even after the furnace stops generating heat.
Switching the thermostat setting from “on” to “auto” should shut the fan down after a few minutes. You’ll still experience a problem if your thermostat has a high temperature setting.
You might feel the temptation to increase your home’s temperature to make it cozier at a faster rate. A high temperature can force the furnace’s blower fan to run for a longer time to accommodate the desired temperature. Try dropping the temperature a few degrees and wait a few minutes to see if that will trigger the fan to stop running.
2. Faulty Limit Switch or Limit Switch on Manual Mode
A furnace fan limit switch turns the blower fan on and off depending on the furnace’s heat output and thermostat settings. A correctly working limit switch will trigger the fan to turn on a few minutes after the thermostat tells the furnace to start producing heat. It should turn off moments after each heating cycle.
A limit switch that doesn’t cause the blower fan to stop working after a heating cycle might be in its manual setting. You can find the limit switch inside the heating system’s panel cover, near the top-right corner.
A white button controls the switch. A pushed-in button means the limit switch is operating in manual mode. To fix this problem and stop the fan from working constantly, the switch needs a reset to its auto mode.
3. Bad Thermostat Wiring
Sometimes, thermostat settings are correct, but the device itself is faulty. If your furnace fan won’t turn off due to a bad thermostat, the motor will continue working even if the thermostat isn’t calling for heat.
You can determine if your thermostat is faulty by removing its face. If the fan stops, the problem is with the face of the thermostat. However, thermostat wiring is the cause of your furnace fan problems if the wiring has fraying from an animal gnawing on it, a poor electrical connection, or flattened sections due to staples.
If thermostat wiring is your problem, you’ll need an HVAC contractor to test the wiring with a multimeter.
4. Tripped Electrical Safety Switch
Furnaces often have safety switches that will cause the blower motor and fan to continue running until someone resets them or the furnace resets them automatically. For instance, a draft temperature switch helps monitor exhaust pipe blockages. If temperatures are high, the switch might trip and keep the motor running but will automatically reset when the temperature drops.
A flame rollout switch prevents flames from returning to the combustion chamber through a gap in the heat exchanger. After tripping this switch, an HVAC professional must manually reset it. Otherwise, the switch stays open and keeps running.
5. Faulty or Incorrectly Set Fan Limit Control
Most modern furnaces have a control board, but older equipment typically uses a fan limit control. The fan limit control serves as a limit switch to shut the electrical gas valve to prevent excessive heat from an overfired furnace. The component also turns the blower motor off and on while the furnace is in heating mode.
Like the limit switch, the fan limit control switch operates in “auto” mode when it’s out. If it pushes in, it switches to “on” mode, causing the fan to blow air continuously.
The fan limit control could also have bimetal with excessive wear. If the component makes the blower motor run instead of turning it off according to its lowest temperature settings, it needs replacing.
6. Overheated Furnace
Sometimes furnaces will put the limit switch into manual mode if the unit is overheating. An overheating furnace usually struggles to produce heat and blow the warmth through air ducts throughout the home.
Clogged furnace filters are one of the top causes of an overheated furnace. The screens trap airborne debris, making your indoor air cleaner, but the pollen, dust, mold spores, and other particles on a dirty screen restrict airflow to the HVAC system. Reduced airflow means a harder working furnace, so it’s best to change air filters regularly.
You can also restrict airflow to the heating unit by closing too many vents on air ducts. Many people assume they can quickly warm the most-used rooms in their homes by shutting the vents in rooms they don’t frequently visit. However, keeping the vents open in every room is better for providing even heating throughout the residence and preventing the furnace from overheating.
Keep Your Furnace Running Correctly with Help from Topline Heating & Air
Whether you need assistance because your furnace fan won’t turn off or you don’t know the airflow on furnace systems, you can count on the expertise of Topline Heating & Air to provide the best solutions. Our premier HVAC company offers outstanding customer care and comprehensive heating and cooling services that we tailor to meet each customer’s needs. We proudly boast hundreds of five-star ratings and 24/7 customer service.
Call (717) 628-6825 to request an appointment with Topline Heating & Air in Columbia, PA.