York Furnace Error Code 3 Flash

A 3 Flash error on a York furnace indicates that a pressure switch did not close when the furnace attempted to start a heating cycle. For first stage heat, the 1LP switch failed to close at the beginning of the cycle. For second stage heat, the 2LP switch did not close within 30 seconds of a second stage call. This prevents the furnace from igniting until the underlying cause is corrected.

The furnace control board will lock out ignition when this error is active, so the burner will not light while the fault is present. This is a protective function. You should not attempt to bypass the pressure switch to force the furnace to run, as the pressure switch confirms that the exhaust system is working correctly before combustion begins.

Cycling power to the furnace may temporarily clear the error code and allow the furnace to attempt another startup sequence. However, if the underlying problem is still present, the 3 Flash code will return quickly during the next heat call. A reset is useful for confirming whether a fault was intermittent, but it does not fix the root cause and should not be used as a substitute for a proper diagnosis.

Some causes of the 3 Flash error are DIY-friendly, such as clearing a blocked vent termination, unclogging a condensate drain, or replacing cracked pressure switch tubing. However, diagnosing a faulty inducer motor or a failed pressure switch typically requires a multimeter and familiarity with furnace components. If you are not comfortable working inside a gas appliance, a licensed HVAC technician should perform the diagnosis.

Repair costs depend heavily on the root cause. Clearing a blocked condensate drain or replacing a short section of pressure switch tubing might cost between $75 and $200 for a service call. Replacing a pressure switch typically runs between $100 and $300 including parts and labor. An inducer motor replacement is a more significant repair, generally falling in the range of $300 to $700 depending on the specific model and labor rates in your area.