Lennox Furnace Error Code 2+7

The 2+7 fault code on a Lennox furnace with control board 100869 means the low pressure switch opened during an ignition trial or while the furnace was actively heating. This switch monitors combustion airflow through the venting system, and when it opens unexpectedly, the control board shuts down the heating cycle as a safety measure. The fault most commonly points to a restricted, blocked, or improperly sized intake or exhaust vent.

The fault code itself represents the furnace's safety system working correctly. When the low pressure switch opens, the control board stops the heating process to prevent combustion from occurring without adequate airflow, which reduces the risk of incomplete combustion or carbon monoxide issues. You should not attempt to bypass the pressure switch, as it is a critical safety component. Keep the furnace off until the underlying cause is resolved.

Resetting the furnace may temporarily clear the fault code and allow the furnace to attempt another ignition cycle, but if the underlying cause has not been corrected, the 2+7 code will return. Repeated resets without addressing the root problem can cause additional wear on components like the inducer motor. The fault should be properly diagnosed and repaired rather than cleared repeatedly through resets.

Homeowners can safely inspect the exterior vent terminations for visible blockages such as ice, debris, or nests and clear them if found. Checking that all accessible vent pipe sections are connected and free of obvious damage is also a reasonable first step. However, diagnosing a failing inducer motor, a faulty pressure switch, or vent sizing errors typically requires specialized tools and knowledge, so a qualified HVAC technician should handle those aspects.

Repair costs vary widely depending on the root cause. Clearing a blocked vent termination may cost little to nothing if done as part of a standard service call, while replacing a pressure switch typically runs in the range of $100 to $300 including parts and labor. An inducer motor replacement is a more involved repair and commonly falls in the range of $300 to $700 or more depending on parts availability and local labor rates.