Furnace locks out with E09, often related to water pressure or flow issues.

Safety: Allow the system to cool before topping up pressure. Hot water can cause scalding.

• Check pressure gauge: Look at the pressure gauge on the front of the Chaffoteaux furnace. If it is below the recommended level (often 1.0 bar cold), the system needs topping up.
• Top up via filling loop: Locate the filling loop (flexible hose or built-in valves). Open the valves slowly until the pressure reaches the target value, then close them firmly. Do not overfill.
• Bleed air: Bleed radiators to remove trapped air, then recheck and adjust pressure.
• Inspect for leaks: Walk around the property and check radiators, valves, and visible pipework for signs of water leakage. Any leak must be repaired.
• Pressure sensor check: If the gauge shows correct pressure but E09 persists, the electronic pressure sensor or its wiring may be faulty and should be replaced by a technician.