The boiler shows a condensate fault or a blocked condensate drain; the unit may shut down.

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

• Check external pipe: Inspect the plastic condensate pipe outside. If it is frozen (common in cold weather), thaw it gently with warm water and lag the pipe to prevent re-freezing.
• Inspect trap (if accessible): With the power off, remove the condensate trap cover or siphon (following the manual). Empty and rinse it with clean water to remove sludge and debris, then refit it securely.
• Verify drainage: Ensure the pipe has a continuous fall to the drain and is not kinked or blocked at the discharge point.
• Reset boiler: After clearing the blockage, reset the boiler and check for normal operation.
• Call a technician if recurring: Persistent condensate faults may indicate an incorrect installation or a damaged Nibe condensate trap that needs replacement.