Samsung Heat Pump Error Code E404

E404 indicates that the compressor sump temperature sensor, which monitors oil temperature at the base of the compressor, has experienced a breakaway condition. This means the sensor or its wiring has lost physical contact with the circuit. The code applies to the digital compressor or fixed 1 compressor on applicable Samsung heat pump configurations. The system raises this fault to prevent the compressor from running without proper thermal monitoring.

Running the heat pump while E404 is active is not recommended. The sump temperature sensor provides protection against overheating or cold-start lubrication issues in the compressor. Without a valid reading from this sensor, the control system cannot properly protect the compressor, and continued operation risks mechanical damage to one of the most expensive components in the system.

A power reset may temporarily clear the E404 code, but it will return if the underlying sensor connection problem has not been resolved. The control board will detect the missing or invalid signal from the sump temperature sensor each time the system cycles and will re-trigger the fault. A lasting fix requires physically inspecting, reattaching, and securing the sensor and its wiring before the error will stay cleared.

If the cause is simply a loose or disconnected sensor connector, a knowledgeable DIYer can inspect and reseat the connector after powering down the unit. However, accessing the compressor compartment and identifying the sump sensor requires some familiarity with heat pump components. If the wiring is damaged or the sensor itself has failed, a qualified HVAC technician should handle the repair to ensure correct reassembly and safe operation.

If the fix is simply reseating a disconnected sensor connector, labor costs could be minimal, typically in the range of $75 to $150 for a service call. If the sensor wiring needs repair or the sensor itself requires replacement, expect total costs in the range of $150 to $400 depending on parts and labor rates in your area. A control board replacement, if needed, would increase costs significantly.