Lennox Furnace Error Code 1+2

Error code 1+2 on a Lennox furnace with control board 100869 means the board detected low flame current during run mode. The flame sense rod is reading a signal below the acceptable threshold while the burner is operating. This causes the furnace to shut down the heating cycle as a safety precaution. The issue is most commonly caused by a dirty or oxidized flame sense rod.

The furnace is designed to shut itself down when it cannot confirm adequate flame current, which is a safety feature that prevents unburned gas from accumulating. You should not attempt to defeat this safety function. Address the fault before relying on the furnace for continuous heating, especially during cold weather.

Resetting the furnace may allow it to attempt another ignition cycle, but the error code will return if the underlying cause has not been corrected. A reset does not fix a dirty or failed flame sense rod or any other component issue. Use the reset only as part of a diagnostic process after cleaning or replacing the rod, not as a standalone fix.

Cleaning the flame sense rod is a repair many experienced DIYers can perform safely when the furnace is powered off. The rod is typically located in the burner assembly and can be cleaned with fine steel wool to remove oxidation. However, if the problem involves gas pressure, wiring, or control board replacement, a licensed HVAC technician should handle the work.

If only the flame sense rod needs cleaning, the cost may be limited to a service call fee, typically in the range of $75 to $150. If the rod needs replacement, parts are generally inexpensive, often in the $15 to $40 range plus labor. A control board replacement is the most expensive possible outcome, with parts and labor potentially ranging from $300 to $600 or more depending on the market.