Boiler shows A1 and stops, often with gurgling noises, especially in cold weather.

Safety first: Switch off the boiler at the control panel before working on the condensate pipe. Do not use naked flames or boiling water.

• Locate the condensate pipe: This is usually a white or grey plastic pipe (21.5mm or 32mm) running from the boiler to a drain, often outside.
• Check for freezing: In freezing weather, feel the external section. If it is very cold and the boiler shows A1, it may be frozen.
• Thaw the pipe: Pour warm (not boiling) water along the length of the external pipe and trap area. You can also use a warm cloth wrapped around the pipe.
• Reset the boiler: Once thawed, reset the boiler and check it runs normally.
• Prevent recurrence: Insulate the external condensate pipe and, if possible, increase its diameter or reroute internally (by a professional) to reduce freezing risk.