Error A05 appears, unit attempts to start but shuts down, sometimes accompanied by fan operation anomalies.

Safety: Disconnect power and ensure the appliance is cool before working on the flue or fan.

• 1. Check flue and terminal: Make sure the Ferroli concentric flue is not blocked or crushed. Clear any debris from the terminal.
• 2. Inspect condensate trap (on condensing models): Remove and clean the condensate trap and hoses. A blocked trap can affect pressure readings.
• 3. Examine pressure switch tubing: Locate the air pressure switch and its silicone tubes. Ensure they are firmly connected, not split, and free of water. Replace any hardened or cracked tubing.
• 4. Listen to fan operation: On startup, the fan should run smoothly. If it does not start, is noisy, or stops abruptly, the fan assembly may be failing and should be replaced.
• 5. Test pressure switch (technician): A professional can test the switch with a manometer or continuity meter to confirm operation and replace it if faulty.

Do not modify or bypass the air pressure switch; it is a critical safety device.