Boiler shows E13, often related to flue or condensate issues, boiler locks out

Safety first: Isolate power. Take care when working with condensate; it is mildly acidic.

• Check condensate pipe: Trace the plastic condensate pipe from the boiler to the drain. Look for kinks, sags, or external sections that may freeze in cold weather.
• Clear freezing (if applicable): If the external pipe is frozen, pour warm (not boiling) water over it and gently massage the pipe to free the ice. Insulate the pipe afterwards.
• Clean condensate trap (engineer task): Remove the trap beneath the boiler, empty it, and rinse with clean water. Refit ensuring seals are correctly seated.
• Check flue slope (engineer task): Confirm the flue has the correct fall back to the boiler as per Sime instructions to allow condensate to drain.
• Reset boiler: After clearing the blockage and refitting the trap, reset the boiler and observe operation.