Navien furnace display shows fluctuating or incorrect water temperature readings

Safety: Turn off power before working on sensor wiring.

• Check sensor connections: Inspect the supply and return thermistor connectors at the PCB and at the sensors. Reseat connectors to ensure good contact.
• Verify sensor mounting: Ensure clip-on sensors are firmly attached to clean pipe surfaces. Clean the pipe and reattach if necessary.
• Separate sensor wiring: Route low-voltage sensor wires away from high-voltage lines to reduce electrical noise.
• Replace suspect thermistor: If readings remain unstable, replace the affected thermistor with a Navien OEM part.