Boiler flue terminal outside shows white staining or dripping water, and there may be damp patches on the wall near the flue.

Safety: Flue gases are hazardous. Do not dismantle the flue yourself.

• Inspect visually: From outside, look for cracks or gaps around the flue terminal and staining on the wall.
• Check condensate pipe: Ensure the condensate drain from the boiler is not blocked, allowing condensate to back up into the flue.
• Do not seal with household products: Avoid using silicone or foam around the flue without following manufacturer guidelines.
• Professional correction: A technician must check flue assembly, slope, and seals, and repair any leaks to maintain safe operation.