Ferroli furnace shows A05 and shuts down; fan may run briefly then stop.

Critical safety warning: A flue overheat fault can indicate dangerous combustion or flue blockage. Turn off the appliance and do not operate it until the flue system has been checked. Risk of carbon monoxide exposure.

User-level checks:

• Inspect outside flue terminal: From outside, ensure the Ferroli flue outlet is not blocked by leaves, snow, nests, or debris. Clear any obvious obstruction without inserting objects into the terminal.
• Check for recirculation: Ensure no structures or vents are directing exhaust gases back towards the flue terminal.
• Reset: Some models have a manual reset flue thermostat inside the casing; this should only be reset after the cause is identified.

Professional-only tasks: Internal flue inspection, flue gas analysis, fan speed verification, and replacement of the flue thermostat or fan must be carried out by a qualified technician familiar with Ferroli appliances.