Samsung Heat Pump Error Code E551

E551 indicates that the indoor heat exchanger EVAP IN piping sensor has detached from its mounting position at the evaporator inlet. This is a mechanical fault where the thermistor is no longer in contact with the refrigerant pipe, causing inaccurate temperature readings. The system raises this code to prevent operating without reliable evaporator inlet temperature data. In most cases, the sensor simply needs to be reattached to the pipe.

Operating the unit with an E551 error is not recommended. Without accurate evaporator inlet temperature data, the system cannot properly manage freeze protection or capacity control, which can lead to coil icing or compressor strain over time. Most Samsung heat pumps will limit or suspend operation automatically when this code is active to protect the system.

If the repair only requires reseating the detached sensor, labor costs for a service call typically range from $75 to $150 depending on your location and the technician. If the thermistor itself needs to be replaced, parts and labor combined generally range from $100 to $250. Costs can be higher if the wiring harness is also damaged or if the unit requires additional diagnostic work.

If you are comfortable removing the indoor unit cover and identifying components inside the air handler, you may be able to locate and reattach the sensor yourself. The repair involves finding the EVAP IN thermistor at the evaporator inlet pipe and pressing it back into its clip or retaping it securely against the pipe. However, if the wiring harness is damaged or the sensor needs to be replaced, a qualified technician should handle the repair.

A power reset may temporarily clear the displayed error, but the E551 code will return if the underlying cause has not been addressed. The sensor must be physically reattached to the evaporator inlet pipe before the fault will clear permanently. After reseating the sensor, cycling power to the unit should allow it to resume normal operation without the code reappearing.