Lennox Furnace Error Code 6 Flashes

Six flashes on a Lennox furnace with control board 103085 indicates a pressure switch cycle lockout. This means the furnace attempted to start multiple times but the pressure switch repeatedly failed to confirm proper draft from the inducer motor. The control board locks the system out as a safety measure. The vent piping, inducer motor, and pressure switch are the primary areas to inspect.

Resetting the furnace by cycling the power or thermostat may temporarily clear the lockout and allow the furnace to attempt ignition again. However, if the underlying problem is not corrected, the pressure switch fault will recur and the lockout will return, possibly after just one or two heating cycles. A reset without repair is not a solution.

Repair costs vary depending on the root cause. Clearing a blocked vent or condensate drain may cost between $75 and $200 in labor if performed by a technician. Replacing a pressure switch typically runs between $100 and $250 including parts and labor. An inducer motor replacement is a more significant repair, generally ranging from $300 to $600 or more depending on the specific motor and local labor rates.

Some causes of this error are DIY-accessible, such as clearing a blocked exterior vent termination, reconnecting a loose pressure switch hose, or clearing a clogged condensate drain. However, testing the pressure switch with a manometer, evaluating inducer motor performance, or replacing components requires basic HVAC tools and comfort working with furnace components. If you are unsure, having a qualified technician diagnose the fault is the safer choice.

Yes, this code represents the furnace protecting itself and your home from potentially unsafe operating conditions. The pressure switch exists to confirm that combustion gases are being properly vented before ignition proceeds. Running the furnace with a compromised venting system or a faulty pressure switch can create risks including incomplete combustion or inadequate flue gas exhaust. Do not attempt to bypass the pressure switch to force the furnace to run.