Display shows A04 and the Ferroli furnace will not start; may occur after power interruptions.

Safety: Ensure the system is cool before adding water to avoid thermal shock. Do not exceed the maximum pressure indicated on the Ferroli data plate.

Steps:

• Check pressure gauge: On the Ferroli control panel, note the current pressure. If below the minimum (often 0.5–0.8 bar), the unit will lock out.
• Top up via filling loop: Locate the Ferroli filling loop (flexible hose or built-in valves). Slowly open the valves and watch the gauge rise to the recommended cold pressure (usually 1.0–1.5 bar). Close the valves fully afterwards.
• Bleed air: After topping up, bleed radiators and any automatic air vents, then re-check pressure and adjust if needed.
• Inspect for leaks: Look around the Ferroli furnace, visible pipework, and radiators for signs of water. Any persistent drop in pressure indicates a leak that must be repaired.
• Reset the unit: Use the reset function on the control panel to clear A04 once pressure is correct.

Professional help: If pressure drops repeatedly with no visible leaks, a technician should check the expansion vessel, pressure relief valve, and the Ferroli pressure sensor for faults.