Ingersoll Rand Furnace Error Code E3.4

E3.4 means the second-stage pressure switch (PS2) is open when the control board expects it to be closed during a call for 2nd stage heat. This switch verifies that the inducer motor is creating enough draft to safely operate the burners at full capacity. The furnace locks out on this code to prevent operation without confirmed proper venting. Common causes include a misoriented switch, a blocked vent, a damaged pressure hose, or a faulty inducer motor.

No. The E3.4 code indicates the furnace has detected a problem with combustion draft safety monitoring and has locked out for this reason. Running the furnace without a confirmed and properly functioning pressure switch bypasses a critical safety layer. The furnace should remain off until the fault is diagnosed and corrected.

Repair costs vary depending on the root cause. Clearing a blocked vent or reseating a loose pressure hose may only require a service call fee, typically in the range of $75 to $150. Replacing a pressure switch usually costs between $100 and $250 including parts and labor. An inducer motor replacement is more involved and can range from $300 to $600 or more depending on the part and local labor rates.

Some causes of E3.4 are accessible to a knowledgeable DIYer. You can check that the PS2 switch is oriented correctly, inspect vent pipes and terminations for visible blockages, and examine the pressure hose connected to PS2 for cracks or disconnections. Electrical testing of the inducer motor, measuring 120VAC from BK to WH, and evaluating the switch itself with a manometer are best handled by a qualified technician.

Cycling power will reset the control board and allow the furnace to attempt another ignition sequence. However, if the underlying problem with PS2, the inducer, or the venting system is not corrected, the E3.4 fault will return during the next call for 2nd stage heat. A power cycle is useful for diagnostic purposes but is not a repair.