Samsung Heat Pump Error Code E504

E504 indicates an error with the indoor unit outlet temperature sensor, meaning the sensor is reading as either open (broken circuit) or shorted (collapsed resistance). This sensor monitors the air temperature leaving the indoor unit and is critical for safe heat pump operation. The code is specific to Samsung heat pump models. The unit will not operate normally until the fault is resolved.

A power reset may temporarily clear the E504 code if the fault was caused by a momentary connection issue, but the error will return if the underlying sensor or wiring problem is not corrected. Repeatedly resetting the unit without addressing the root cause can delay necessary repairs and may affect system reliability. A proper diagnostic check of the thermistor and wiring is needed for a lasting fix.

Repair costs vary depending on the root cause. Replacing an NTC outlet thermistor typically falls in the range of $50 to $150 for parts, with labor adding $75 to $200 depending on your region and technician rates. If the indoor unit PCB is at fault, parts alone can range from $150 to $400 or more. A service call for diagnosis is usually charged separately at $75 to $150.

A knowledgeable DIYer can check the sensor connector for looseness and inspect the wiring harness for obvious damage without special tools. However, properly testing the thermistor resistance and diagnosing a PCB fault requires a multimeter and familiarity with reading component specifications. If the sensor or PCB needs replacement, a certified HVAC technician is recommended to ensure correct parts and safe reassembly.

The heat pump will typically stop normal operation when E504 is active precisely to protect the system. Attempting to bypass or ignore this fault is not recommended, as the outlet temperature sensor plays a role in managing defrost cycles and preventing overheating of refrigerant circuit components. Leave the unit off until the sensor fault is diagnosed and repaired.