Boiler indicates flue sensor or safety thermostat fault, may lock out

Safety: A tripping flue safety device can indicate dangerous flue conditions. Do not bypass or short this device.

• Check flue route: Ensure the flue is not blocked or damaged. Look for signs of overheating or discoloration around the flue path.
• Inspect thermostat: Locate the flue thermostat on the flue hood or casing. Check that its wiring is intact and terminals are tight.
• Reset (if manual): Some flue stats have a manual reset button. Once cooled, press to reset. If it trips again, stop using the boiler.
• Replace thermostat: If the thermostat is open-circuit and the flue is confirmed clear, a technician should replace it with a Riello-approved part.