Furnace displays E11, burner does not light, fan may run.

Safety: Turn off gas and power. Wait for the furnace to cool.

Steps:

• Visual inspection: Locate the ignition electrode near the burner. Check for cracks in the ceramic insulator, broken tip, or heavy carbon buildup.
• Clean electrode: Gently clean the metal tip with fine sandpaper. Do not bend the electrode unless adjusting the gap per Cointra specifications.
• Check ignition cable: Inspect the high-voltage cable from the control board to the electrode for burns, cuts, or loose connections. Reseat both ends.
• Observe spark (advanced): With covers in place and viewing window accessible, restore power and call for heat. Look for a strong blue spark at the electrode. If no spark is visible, the electrode, cable, or ignition transformer may be faulty.

Professional service: Replacement of the ignition transformer or control board should be done by a qualified technician following Cointra procedures.