Sub-Zero Refrigerator Error Code Control board light - slow flash

The slow flash on the control board indicates that the liquid line thermistor is open or disconnected. This thermistor monitors the temperature of the liquid refrigerant line and sends that data to the control board. When the board receives no valid signal, it triggers this fault indicator. The issue is either a failed thermistor, a broken wire, or a loose connector at the board.

A reset may temporarily clear the fault display, but the slow flash will return if the underlying problem is not resolved. The control board will re-detect the open circuit on the liquid line thermistor and re-flag the fault. The thermistor connection and component condition must be inspected and corrected to permanently clear the code.

If only the thermistor needs replacement, parts typically range from around $30 to $80 depending on the specific model, with labor adding $100 to $200 or more depending on your location and the service provider. If the control board is at fault, that repair is considerably more expensive, with parts alone ranging from $200 to $600 or higher. Getting the thermistor and wiring diagnosed first helps avoid unnecessary board replacement costs.

A knowledgeable DIYer can check whether the thermistor connector is simply unplugged and reseat it if so. Testing thermistor resistance with a multimeter at the thermistor itself requires access to the component and knowledge of the expected resistance values: 30K-33K ohms at 32 degrees Fahrenheit or 8K-12K ohms at 77 degrees Fahrenheit. If the connector is secure and the thermistor reads open or far outside those ranges, replacing the thermistor is a straightforward repair for someone comfortable working on refrigerators. Control board replacement should generally be left to a qualified technician.

The refrigerator may continue to run while this fault is active, but the control board is operating without accurate liquid line temperature data. This can affect how efficiently the refrigerant cycle is managed and could lead to temperature inconsistencies over time. It is best to address the fault promptly to avoid potential food safety issues or additional strain on refrigeration components.