Lennox 40L81 / LB94701A Flame Sensor

Product Specifications:

The flame sensor is a device located at the burner assembly and can be found in furnaces, boilers and other gas-burning appliances.  

The purpose of the flame sensor is to confirm that whenever the gas valve is open, a fire or flame is present. If there were nothing to ignite, once gas is emitted, a dangerous build-up might occur. Flame sensors have a short time in which to detect a flame. If no flame is detected, the unit will automatically shut down.  If this shutdown happens after a few times, a safety lockout usually happens that shuts the unit down for more than an hour.  In the case of carbon build-up on a dirty flame sensor, a furnace will keep shutting down - a common complaint by homeowners.  Carbon build-up is often caused by dusty particles in the air that burn to a sensor, especially if the furnace is located in areas that typically collect a lot of dust, such as basements and attics.

Flame sensors can be cleaned by using emery cloth and steel wool. 

HeatingPartsCanada carries a wide selection of flame sensors.  If you do not see the part or need help cross-referencing, give our friendly staff a call at 1-844-81-PARTS