Boiler displays E13, condensate may be visible around the base, burner may not start.

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

• Inspect condensate pipe: Follow the plastic condensate pipe from the boiler to the drain. Check for kinks, sagging, or external freezing in cold weather.
• Clean trap: Remove the condensate trap/siphon under the boiler. Empty and rinse with clean water. Remove sludge or debris.
• Check slope: Ensure the condensate pipe slopes continuously downward to the drain with no upward loops.
• Defrost if frozen: If the external pipe is frozen, thaw gently with warm (not boiling) water and insulate the pipe afterwards.
• Reassemble and test: Refit the trap, ensure all seals are tight, then reset the boiler and check for leaks and normal operation.