Lennox Furnace Error Code 2+3

The 2+3 flash code on a Lennox furnace means the low fire pressure switch was detected in the open position. This fault applies to 80% efficiency models and indicates the furnace control board did not confirm adequate combustion airflow during startup. The furnace shuts down as a safety measure to prevent operation without proper draft.

Yes, the furnace intentionally locks out when this code appears to prevent operation without verified combustion airflow. Running a furnace with a blocked exhaust could allow combustion gases to accumulate, creating a carbon monoxide hazard. Do not attempt to bypass the pressure switch and address the root cause before restoring furnace operation.

Resetting the furnace by cycling power may temporarily clear the fault and allow the furnace to attempt another startup, but if the underlying cause is not corrected, the 2+3 code will return. A reset is useful for confirming whether the problem is intermittent, but it is not a fix. The root cause, whether a blocked vent, faulty switch, or damaged hose, must be identified and corrected.

Start by inspecting the exhaust flue termination on the outside of your home for any blockage such as ice, debris, or a bird nest. If the vent is clear, check the pressure switch hose for cracks or loose connections. If those items check out, the pressure switch or inducer motor may need testing and possible replacement by a qualified technician.

If the issue is a blocked exhaust that you can clear yourself, the repair may cost nothing. If a pressure switch replacement is needed, parts and labor typically range from $150 to $350. An inducer motor replacement is more involved and can range from $400 to $800 or more depending on the specific model and labor rates in your area.