Dishwasher displays E9; water may overheat or remain cold depending on failure mode

Safety first: Disconnect mains power and allow the machine to cool completely before working near the heater.

• Locate the NTC: The NTC sensor is usually clipped into the sump or attached to the heater housing. Access it from the bottom of the dishwasher.
• Inspect connection: Check that the NTC plug is firmly seated and that there is no corrosion or moisture in the connector.
• Measure resistance: Remove the NTC and measure its resistance at room temperature with a multimeter. Compare with service specifications (commonly tens of kΩ). A reading of 0 Ω (short) or infinite (open) indicates a faulty sensor.
• Replace if faulty: Install a new NTC sensor compatible with your De Dietrich model, ensuring it is properly seated and sealed.
• Check wiring and board: If the NTC tests good but E9 persists, inspect the wiring harness for damage and consider control board diagnosis by a professional.