Boiler locks out with E07; may indicate flue temperature too high or flue sensor fault.

Safety: Turn off power and allow the boiler to cool. Never operate the boiler with a suspected flue blockage.

• Check exhaust vent: Inspect the entire length of the exhaust vent for obstructions, sagging, or disconnections. Outside, clear any debris or ice from the termination.
• Inspect flue sensor: Locate the flue gas temperature sensor on the flue outlet inside the boiler. Ensure it is firmly mounted and the wiring is intact.
• Reset and observe: After clearing any obvious vent issues, reset the boiler. If E07 returns quickly, the sensor may be faulty or combustion may be abnormal.

Because flue overheat can indicate dangerous combustion conditions, have a qualified technician perform a combustion analysis, verify fan operation, and replace the flue temperature sensor or adjust combustion as required.