Condensate fault, boiler shuts down with drain or condensate error, possible gurgling noises

Safety: Condensate is mildly acidic. Wear gloves and eye protection when handling. Turn off power before opening the trap.

• Inspect condensate pipe: Follow the plastic condensate pipe from the boiler to the drain. Check for kinks, sags, or external freezing (in cold weather). Thaw gently with warm towels if frozen; do not use open flame.
• Clean condensate trap: Locate the Viessmann condensate trap/siphon beneath the heat exchanger. Place a container underneath, remove the trap, and rinse it thoroughly with clean water to remove sludge and debris.
• Check internal hoses: Ensure all internal condensate hoses are securely connected and not blocked.
• Reassemble and test: Refit the trap, ensuring seals are correctly seated. Restore power and reset the boiler. Listen for normal condensate draining during operation.
• Persistent faults: If F13 returns, a technician should inspect the heat exchanger condensate outlet and verify proper pipe sizing and fall.