Boiler locks out with E08, sometimes accompanied by gurgling noises, especially in cold weather.

Safety first: Turn off the boiler before working on the condensate system. Condensate is mildly acidic; wear gloves and eye protection.

User-level checks:

• Inspect the external condensate pipe for freezing (bulging or ice). Thaw gently with warm water or a warm cloth; do not use naked flames.
• Once thawed, reset the boiler and see if it operates normally.

Technical checks (qualified personnel):

• Remove and clean the condensate trap/siphon; flush out sludge and debris.
• Check that the condensate pipe has adequate fall and is correctly sized per Chaffoteaux installation instructions.
• Ensure the trap is refilled with clean water before refitting to maintain the seal.
• Inspect internal condensate channels in the heat exchanger for blockage and clean if accessible.

Consider upgrading or insulating the external condensate pipe to reduce the risk of future freezing.