Furnace attempts to start, fan runs, then stops with E03 on the display.

Safety: Disconnect power before removing the front cover. Do not operate the furnace with the sealed chamber open.

• Check flue terminal: From outside, ensure the Chaffoteaux flue terminal is clear of obstructions (ice, nests, foliage). Remove any blockage without damaging the terminal.
• Inspect pressure tubes: Locate the air pressure switch near the fan. Check the silicone tubes from the fan/venturi to the switch for splits, kinks, or disconnections. Refit or replace damaged tubing.
• Check condensate in tubing: If the furnace is condensing, water can accumulate in the pressure tubes. Remove the tubes carefully and blow through them to clear moisture. Reconnect securely.
• Fan operation: With the casing back on, restore power and call for heat. Listen for the fan starting. If the fan is noisy, slow, or fails to start, the fan assembly may be failing and should be replaced by a professional.
• Reset: After checks, reset the furnace. If E03 persists, the air pressure switch or control board may be defective and must be tested and replaced by a qualified Chaffoteaux technician.