Lennox Furnace Flame Sensors
Lennox replacement flame sensors for gas furnaces, listed by Lennox part number: 52W29 (LB-74940A), 20J90, 20J91, 69W43, 79J22, 49M84, 43K53, 28M97, 17J56, 18G89 and 51M14, plus the 40L81 sensor kit and the 62K50 flame sensor and ignitor kit. Check your furnace manual or the old sensor for the number.
Browse all furnace flame sensors, or see Lennox maintenance kits.
Lennox flame sensor guide: finding the right part ▾
Find the right sensor
Flame sensors differ in rod length, bracket and connector, so match the Lennox part number. Find your furnace model and serial number on the rating plate inside the burner door, then look up the flame sensor in the parts list, or read the number on the old sensor.
Signs and safety
A common sign of a dirty or failing flame sensor is a furnace that lights, then shuts the burners off after a few seconds and tries again. A technician may clean a dirty sensor, but a cracked porcelain insulator or damaged rod means it should be replaced. This is gas appliance work, so have a licensed gas technician diagnose the furnace and replace the sensor.
