Heater displays H20; water may be too hot or unit may shut down on high temperature.

Scalding risk: Do not use hot water until the cause is identified. Test water temperature carefully.

• 1. Lower set temperature: Reduce the set temperature on the controller and test again.
• 2. Increase flow:
  • Open the hot tap more fully.
  • Clean aerators and shower heads to improve flow.
• 3. Clean inlet filter: Ensure the cold water inlet filter is clean to maintain proper flow.
• 4. Inspect outlet thermistor: Follow steps similar to H07 to check and, if necessary, replace the outlet temperature sensor.
• 5. Descale heat exchanger: Perform a descaling procedure if the unit is in a hard‑water area or has never been descaled.
• 6. If H20 persists: The gas valve modulation or PCB control may be faulty and should be checked by an authorized Panasonic technician.