Boiler shows E05 and does not heat; fan (on combi models) may not start

Safety first: Turn off gas supply (if applicable) and isolate electrical power. Allow the boiler and flue to cool completely.

Steps to check:

• Access the flue sensor: Remove the combustion chamber cover according to the Kospel service instructions. Locate the flue gas NTC sensor clipped to the flue or heat exchanger outlet.
• Inspect for damage: Check the sensor body and cable for signs of overheating, melting, or mechanical damage. Replace if damaged.
• Clean the sensor: If the sensor tip is covered in soot or condensate residue, gently clean it with a soft cloth. Do not use abrasive materials.
• Check wiring and connectors: Ensure the sensor wiring is not touching hot surfaces and that connectors are firmly seated on the control board.
• Test and reset: Restore power and gas, then reset the boiler. If E05 returns, the sensor or control board may be faulty and should be tested by a professional.

When to call a technician: Work inside the combustion chamber and flue system should generally be performed by a licensed gas technician familiar with Kospel boilers.