Kenmore water heater displays E40 and water temperature is much hotter or colder than the setpoint

Safety: Turn OFF power before accessing sensors or control board.

• Verify parts: Confirm that any recently replaced temperature sensors are genuine or compatible Kenmore parts with correct resistance curves.
• Check sensor placement: Ensure upper and lower thermistors are installed in the correct positions and firmly against the tank or in their wells.
• Inspect wiring: Verify that the upper sensor is plugged into the upper sensor connector and the lower into the lower connector on the control board. Correct any cross-connection.
• Control reset: Perform a factory reset or calibration procedure if provided in the service manual.
• Replace control board: If sensors and wiring are correct and E40 persists, replace the main electronic control board.