Lennox Furnace Error Code E266

E266 indicates a soft lockout caused by exceeding the maximum number of calibration retry attempts. The furnace tried to complete its internal calibration routine multiple times and failed each time, so it shut down to prevent continued cycling. This code is always tied to an underlying fault, specifically E228, which must be diagnosed and resolved first.

Resetting the furnace will clear the lockout temporarily and allow the calibration routine to run again. However, if the underlying cause of the E228 fault is not corrected, the furnace will fail calibration again and reissue E266. A reset without a repair is only a short-term measure.

Repair costs depend entirely on what is causing the repeated calibration failure. Clearing a condensate blockage is typically inexpensive, ranging from around $75 to $150 for a service call. Replacing a pressure switch generally falls in the $100 to $300 range including parts and labor. Inducer motor or control board replacements can cost significantly more, often between $300 and $700 or higher depending on the specific components and labor rates in your area.

Some causes, such as a clogged condensate drain or a disconnected pressure tube, can be addressed by a knowledgeable homeowner. However, diagnosing the root cause requires understanding the E228 fault code, which may involve testing pressure switches and inspecting the inducer motor. If you are not comfortable working with HVAC components and electrical circuits, a licensed technician is the safer choice.

E266 is a soft lockout, meaning the furnace has already stopped running on its own as a protective measure. The furnace will not operate normally while this code is active. You should not attempt to force the system to run repeatedly without identifying and correcting the root cause, as doing so may mask a more serious underlying problem.