Display shows A09, unit refuses to start, often after a power outage or wiring work.

Safety: Disconnect power and close water supply before removing any water connections.

• Check DHW demand: Open a hot tap and observe if the flow indicator on the display (if available) activates. If not, the flow sensor may not be detecting flow.
• Clean inlet filter: At the cold water inlet of the Fondital heater, remove and clean any mesh filter to restore proper flow.
• Inspect flow sensor: Locate the DHW flow sensor or flow switch body. Remove it carefully and check for debris or scale that may prevent movement of the internal turbine or paddle. Clean and reinstall with new seals if needed.
• Check wiring: Ensure the sensor connector is firmly seated on the control board and that cables are not damaged.
• Replace sensor: If A09 persists and wiring is sound, replace the DHW flow sensor with a compatible Fondital part.