Navien unit displays E051 and stops; often related to water temperature sensing.

Safety: Turn OFF power and close water valves before working on sensors attached to water lines.

Steps:

• 1. Inspect sensor connection: Locate the cold water inlet temperature sensor (thermistor) on the inlet pipe. Ensure it is firmly attached and the wiring connector is secure.
• 2. Check for corrosion: Look for corrosion or moisture around the sensor connection. Dry and clean as needed.
• 3. Power reset: After reseating the connector, restore power and test. If E051 returns, the sensor is likely faulty.

Replacing the inlet thermistor is typically straightforward but may require draining a small amount of water. If you are not comfortable with plumbing work, contact a professional.