Lennox Furnace Error Code E334

E334 means the integrated control board has detected that the Y1 relay is stuck in the on position. The Y1 relay is an internal component of the control board that manages the cooling or compressor signal circuit. When this relay fails to de-energize as expected, the control board logs E334 and flags the fault. Resolving this error requires replacing the integrated control board.

A power reset will not clear E334 if the Y1 relay is physically stuck in the closed position. Because the fault is caused by a hardware failure inside the integrated control board, the relay contacts remain welded regardless of control signals. The error will return immediately after reset until the faulty control board is replaced.

Since E334 requires replacement of the integrated control board, costs typically include the part and labor for the board swap. Integrated control boards for Lennox furnaces generally range from around 150 to 500 dollars depending on the specific model, and labor charges from an HVAC technician can add another 75 to 200 dollars depending on your region and service provider. Total repair costs commonly fall in the range of 225 to 700 dollars.

The required repair for E334 is replacement of the integrated control board, which is a moderately complex task involving disconnecting and reconnecting multiple wiring harnesses and electrical connections. DIYers with electrical experience may be able to perform the swap, but working inside a furnace involves line voltage and gas system components. It is recommended to have a qualified HVAC technician perform this repair to ensure safety and correct installation.

An E334 fault indicates an internal control board failure and the furnace should not be operated until the issue is resolved. A stuck Y1 relay can cause unintended signaling to connected cooling or compressor equipment, which could result in improper system operation or component damage. Shut the furnace down and schedule a service call promptly.