E18 error and the unit indicates resin sensor or quality sensor fault (on models with integrated water quality monitoring).

Safety: Turn off power and close inlet valve before removing any in-line sensors.

• Locate sensor: Identify the Hansgrohe water quality sensor, typically installed in the outlet manifold or a bypass loop.
• Clean sensor: Remove the sensor and soak the tip in a mild vinegar solution to dissolve scale. Rinse thoroughly with clean water.
• Inspect O-rings: Replace any damaged O-rings to prevent leaks when reinstalling.
• Check cable: Verify that the sensor cable is intact and firmly connected to the control board.
• Test operation: Reinstall the sensor, restore water and power, and run water through the system. If E18 persists, replace the water quality sensor.