Furnace shuts down shortly after ignition; display shows E03 and burner stops.

Safety: Turn off power and gas before opening the combustion chamber. Allow the furnace to cool completely.

• Inspect flame sensor and wiring: Locate the flame sensor (ionization rod) on the burner. Remove and clean it with fine abrasive pad to remove oxidation. Check the sensor wire for damage and ensure it is firmly connected to the control board.
• Check grounding: Verify that the furnace chassis is properly grounded. Tighten the ground screw and clean any corrosion at the ground connection.
• Clean burner and primary heat exchanger: Remove the burner assembly and brush off rust, dust, and debris. Use a vacuum with a brush attachment to clean the burner and accessible parts of the heat exchanger. Do not damage gaskets.
• Observe flame: After reassembly, restore power and gas. Observe the flame through the sight glass. The flame should be stable and mostly blue. Yellow, lifting, or blowing-off flames indicate gas or air issues that require a technician.

If E03 continues after cleaning and checking connections, contact a Kospel service center to check gas pressure and possibly replace the flame sensor or main control board.