Samsung Heat Pump Error Code E478

E478 indicates that the sump temperature sensor on the second fixed compressor has broken away from its mounted position or lost its connection. The sump sensor monitors oil temperature at the base of the compressor to prevent thermal damage. The system logs this fault when it detects the sensor is no longer providing a valid reading from its intended location. The fix typically involves physically reattaching, reseating, or replacing the sensor and its mounting hardware.

Operating the system without a functioning sump temperature sensor on compressor 2 is not recommended. The sensor is a protective component, and running the compressor without accurate sump temperature monitoring risks undetected overheating and potential compressor damage. It is best to have the fault addressed promptly to avoid more costly repairs.

If the repair only requires reseating the sensor and securing its mount, labor costs are typically modest, often in the range of $75 to $150 depending on the service provider and location. If the sensor itself needs replacement, parts and labor combined could range from $150 to $400 or more. A technician's diagnostic visit is usually required first to confirm the exact nature of the fault.

In some cases, a qualified technician can resolve E478 simply by reseating the sensor and securing its mounting clip, which does not require parts. However, working on heat pump compressors involves refrigerant systems and high-voltage components, so this repair should be performed by a certified HVAC technician. Attempting repairs without proper training or tools can create safety hazards and may void equipment warranties.

A power reset may temporarily clear the fault code from the display, but the error will return if the sensor is still physically detached or disconnected. The underlying cause, meaning the sensor breakaway condition, must be corrected before the fault will stay cleared. Resetting without repairing should only be done for diagnostic purposes, not as a solution.