Error A09 appears, unit may lock out during operation, sometimes after long runs at high temperature.

Safety: Turn off gas and power. Do not operate the heater with a suspected flue problem.

• 1. External flue inspection: Check that the Ferroli flue terminal is installed to manufacturer clearances and is not obstructed. Look for signs of condensation staining or corrosion.
• 2. Internal flue path: A qualified technician should inspect the entire flue run for blockages, disconnections, or incorrect slopes.
• 3. Check flue thermostat: Locate the flue overheat thermostat and test for correct operation. Replace if it trips at too low a temperature or is permanently open.
• 4. Combustion check: A gas-safe technician must verify burner pressure and combustion values (CO/CO2) and adjust or replace the gas valve if necessary.

Because flue issues are a serious safety risk, professional service is strongly recommended for A09 faults.