Goodman HVAC Error Code 4

Error code 4 on a Goodman furnace means the control board detected an open main limit switch during operation. The main limit switch is a safety device that trips when the heat exchanger temperature exceeds a safe limit. This causes the furnace to shut down the burners to prevent overheating damage. The most common cause is restricted airflow from a dirty filter or blower issue.

Yes, error code 4 should be taken seriously because it means the furnace reached unsafe internal temperatures and shut itself down to prevent damage. In most cases the cause is airflow restriction, which is correctable. However, a cracked heat exchanger is a potential underlying cause that can allow combustion gases to enter the living space and requires immediate professional inspection before further furnace use.

Repair costs depend on the root cause. A replacement air filter costs very little, typically in the range of a few dollars to around $30. A new run capacitor for the blower motor generally runs between $15 and $60 for the part. A replacement limit switch can range from $10 to $50 for the part, with labor costs varying by region. If a cracked heat exchanger is found, that repair or heat exchanger replacement can range from several hundred to over a thousand dollars depending on the unit.

Some causes of error code 4 are DIY-friendly. Start by replacing the air filter and making sure all supply and return registers are open and unobstructed. If the furnace still trips the limit after restoring airflow, further diagnosis involving the blower motor, capacitor, or limit switch itself is best handled by a technician, especially if a cracked heat exchanger is suspected.

Resetting the furnace may temporarily clear the error and allow the unit to restart, but the code will return if the underlying cause is not corrected. The limit switch itself may reset automatically once it cools down, but repeated tripping accelerates wear on the switch and the heat exchanger. Always identify and correct the root cause before relying on a reset.