Boiler shows E09 and shuts down; often associated with flue gas temperature or sensor fault

Safety: Turn off power and gas. High flue temperatures can be dangerous; do not operate the boiler until the cause is identified.

• Inspect flue gas sensor: Locate the flue gas temperature sensor on the flue outlet of the Crown boiler. Check that it is firmly attached and wiring is intact.
• Check venting: Inspect the flue for blockages, sagging, or signs of overheating (discoloration, melting). Clear any obstructions.
• Clean heat exchanger (visual): Look through the burner opening for heavy soot or scale on the heat exchanger surfaces. Excessive buildup requires professional cleaning.
• Reset: After inspection, restore power and reset the boiler. If E09 recurs, the flue gas sensor or combustion settings must be checked and adjusted by a qualified technician using proper instruments.