LG Heat Pump Error Code E355

E355 indicates a suction temperature sensor error caused by either an open circuit or a short circuit condition in the thermistor that monitors refrigerant temperature at the compressor inlet. The control PCB detects a resistance value outside the expected range and triggers the fault. The system typically disables the compressor until the sensor issue is diagnosed and corrected.

It is not advisable to continue operating the heat pump while E355 is active. The suction temperature sensor provides data the system needs to protect the compressor from liquid refrigerant slugging and other harmful conditions. Running without accurate sensor data risks compressor damage, which is a significantly more expensive repair than fixing the sensor itself.

A power reset may temporarily clear E355, but the fault will return if the underlying sensor, wiring, or connector problem is not resolved. Resetting without diagnosis is not a fix and can delay identifying a condition that may cause further component damage. The fault should be properly diagnosed by measuring sensor resistance and inspecting all connectors before relying on a reset.

Some causes of E355 are DIY-accessible, such as reseating a loose sensor connector or inspecting visible wiring for damage. However, if the thermistor itself needs replacement or the fault involves refrigerant-side components, a qualified HVAC technician should perform the repair. Working on a heat pump system without proper training and tools carries risk of refrigerant exposure and equipment damage.

Repair costs vary depending on the root cause. Reseating a connector or replacing a wiring harness segment is typically a low-cost repair in the range of $75 to $200 for labor. A suction temperature thermistor replacement generally falls in the $100 to $300 range including parts and labor. If the PCB is at fault, costs can rise to $400 to $900 or more depending on the unit model and parts availability.