How Can a Furnace Temperature Sensor Help Your House?

The furnace temperature sensor, also known as the flame sensor, is a vital component of safety if you have a gas furnace and is often a part of common winter HVAC service. Flame sensors are present on newer furnaces that utilize electronic igniters instead of the older pilot lights of the past.

How the Furnace Temperature Sensor Works

  • When your thermostat signals the furnace for heat, the gas valve opens and the electronic igniter lights the main gas burner. Mounted directly in the main burner, the flame sensor generates a specific electronic voltage when exposed to the burner flame. This voltage tells the furnace central processor that the gas burner has been safely ignited, and gas flow continues normally.
  • If the voltage reading from the sensor indicates that the burner flame is not present or that its temperature is too low, the main gas valve is instantly shut off. This prevents dangerous, unburned flammable gas from leaking into the house.
  • After startup, the furnace temperature sensor continuously monitors the burner flame temperature as the heating cycle continues. The sensor will shut down the gas flow should the flame subsequently go out for any reason.

What Happens if It Doesn’t Work?

A common symptom of furnace-sensor issues is that the main burner flame will initially light up for eight to 10 seconds and then abruptly shut off again. The furnace will then blow cold air.  If the sensor shuts down the flame three times consecutively, the furnace will go into safety lockout mode and will not open the gas valve again until the problem is resolved.

Why Do Sensors Fail?

A furnace sensor is exposed to heat-related wear and tear that may eventually degrade accurate sensing. If the sensor is simply dirty and coated with carbon residue, cleaning the existing sensor may be part of common winter HVAC service by a qualified heating specialist. Alternatively, a defective sensor may require routine replacement at some point during the service life of the furnace.

Cleaning or replacing a defective furnace temperature sensor is common winter HVAC service provided by Paitson Bros. Safe, efficient heating has been our business in Terre Haute since 1922.

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