Boiler shows E20, often associated with condensate issues or flue-related lockouts.

Safety: Condensate is mildly acidic. Wear gloves and eye protection when handling.

• Check external condensate pipe: Look for kinks, sagging, or freezing (white frost) on the plastic pipe leading outside or to a drain.
• Thaw frozen pipe: Pour warm (not boiling) water over the frozen section until thawed. Insulate the pipe to prevent recurrence.
• Clean condensate trap: Isolate power, remove the trap beneath the boiler, empty and rinse it, then refit ensuring seals are correct.
• Prime the trap: Pour a small amount of clean water into the trap to ensure the siphon is filled before restarting.