Boiler frequently locks out during very cold weather, condensate pipe outside is icy.

Safety: Do not use boiling water directly on plastic pipes; they may crack.

• Thaw pipe: Pour warm (not boiling) water over the external condensate pipe and trap area, or use a hot water bottle or heat pack to gently thaw the ice.
• Clear trap: Once thawed, remove and clean the condensate trap under the Defro boiler, then refit and refill with water.
• Insulate pipe: Lag the external condensate pipe with weatherproof insulation to reduce future freezing.
• Reroute (long-term): Consider having a professional reroute the condensate to an internal drain with minimal external exposure.