Hansberger Refrigeration Blog: Your AC Repair Resource

How to React If You Find Your Home’s Furnace Overheating

While safe furnace operation is a vital asset for home comfort, a furnace overheating can be both hazardous and incur damage that requires expensive repairs. Gas-fired furnaces are made to operate within a very specific, safe temperature range. When the entire furnace or an individual component inside the unit gets too hot, a malfunction is occurring. An overheating furnace may present a definite fire hazard. Even without a fire, overheating may permanently damage critical system components, including the heat exchanger, which is the most expensive part in the furnace.  Typical causes of a furnace overheating include:

  • A dirty air filter restricting proper system airflow.
  • A defective blower not circulating sufficient airflow.
  • Blockage in system ductwork.
  • A sensor that detects that the burner flame is defective and shutting off the furnace.
  • A limit switch that is defective.

What to Do If You Discover Your Furnace Overheating

Signs of a furnace running too hot should never be ignored. If you notice any of the following symptoms of overheating, turn off the furnace at the thermostat and call for professional HVAC service.

  • An odor of something overheating or burning coming from the furnace itself or from air circulating through the HVAC vents in the house.
  • Unusual noises or humming sounds emanating from the furnace unit. The large electric motor that drives the blower may be defective and overheating. This can produce noticeable noise, as well as a pungent odor in the system’s airflow.
  • The furnace starts and then turns itself off before the normal heating cycle has completed. The limit switch inside the furnace may have detected excessively high internal temperatures and automatically shut down the furnace. If multiple limit-switch actuations occur within a certain time frame, the system may impose a “hard shutdown.” In that case,  the furnace cannot be restarted at the thermostat. A qualified HVAC technician will be required to resolve the problem, then take specific steps to reset the high-limit switch and restart the unit.

For qualified service to diagnose a furnace overheating and restore safe operation, contact the professionals at Hansberger Refrigeration and Electric Company.