Display shows E9; unit may overheat and shut down, sometimes with noise from boiling water.

Safety: Turn off the appliance and allow it to cool completely. Do not reset repeatedly without finding the cause.

• Check water flow: Open hot taps fully and verify strong flow. Clean inlet filters and tap aerators if flow is weak.
• Inspect isolation valves: Ensure all service valves on the heater are fully open.
• Look for scale signs: Popping or kettling noises indicate limescale in the heat exchanger. Professional descaling is recommended.
• Reset safety limiter (if accessible): Some Junkers models have a manual reset overheat thermostat on the heat exchanger. Only reset once after cooling; if it trips again, call a technician.