Ferroli furnace stops and displays A03, often after running for some time; unit may feel very hot.

Safety: Turn off power and allow the furnace to cool completely before touching any pipework. System water can be scalding.

Steps:

• Check system pressure (for hydronic/boiler-type furnaces): On the Ferroli gauge, ensure pressure is within the recommended range (typically ~1.0–1.5 bar when cold). If low, top up via the filling loop following the user manual.
• Bleed radiators and air vents: Airlocks reduce flow and cause overheating. Use a radiator key to bleed air until water flows steadily.
• Verify all valves are open: Ensure isolation valves under the Ferroli unit and on nearby pipework are fully open.
• Check circulation pump: With power on and a call for heat, listen for the Ferroli pump running. If silent or excessively noisy, the pump may be seized. Some pumps have a front screw to manually free the shaft (follow Ferroli instructions).
• Reset overheat thermostat: Many Ferroli models have a manual reset button on the overheat stat inside the casing. Once cooled, press gently until it clicks.

Professional help: If A03 recurs, a technician should test pump performance, verify correct system design/flow, and replace the overheat thermostat or NTC sensor if faulty.