Furnace shows E13, may be associated with condensate or flue issues.

Safety: Isolate power. Condensate is mildly acidic; wear gloves and eye protection.

• Inspect condensate pipe: Follow the plastic condensate pipe from the furnace to the drain. Check for kinks, sags, or external freezing in cold weather.
• Defrost (if frozen): If the external section is frozen, pour warm (not boiling) water over the pipe until thawed. Insulate the pipe afterward.
• Clean condensate trap: Place a container under the trap, remove it, and flush thoroughly with clean water. Ensure the internal siphon is reassembled correctly to maintain the water seal.
• Check for leaks: Refit the trap securely and check for drips during operation.
• Reset: Restore power and reset the furnace. If E13 persists, a condensate sensor or internal blockage may require professional attention.