Furnace displays C1, fan runs but burner does not ignite or shuts down quickly

Safety first: Isolate electrical power and shut off gas. Do not operate the furnace with suspected flue blockage due to risk of carbon monoxide.

• 1. Check air intake and flue: From outside, inspect the concentric flue terminal for obstructions such as leaves, nests, or ice. Clear any blockage carefully. Ensure the terminal is not covered or restricted.
• 2. Inspect fan compartment: Remove the front cover and combustion chamber cover as per Junkers instructions. Check the fan wheel for dust buildup or foreign objects. Clean with a soft brush and vacuum.
• 3. Test fan rotation: With power off, spin the fan wheel by hand. It should rotate freely without grinding or excessive play. If stiff or noisy, the fan assembly may need replacement.
• 4. Electrical checks: Verify that the fan connector is fully seated on the main PCB. Inspect wiring for damage. With power on and a call for heat, confirm that the fan receives the correct voltage (only if you are trained and using proper safety precautions).
• 5. Fan speed feedback: Many Junkers fans use a Hall sensor for speed feedback. If the fan runs but the control reports incorrect speed (C1), the sensor or PCB may be faulty. Replacement of the fan assembly is often required.
• 6. Do not bypass safety: Never bypass airflow or fan monitoring circuits. If you cannot restore normal fan operation, contact an authorised Junkers technician.