Boiler displays A1 and stops, often accompanied by gurgling sounds; condensate may not be draining.

Safety first: Turn off power before working near water or condensate pipework. Do not use naked flames to thaw pipes.

User actions (safe):

• Locate the external condensate pipe (usually white plastic) and check for freezing in cold weather.
• Thaw a frozen pipe by pouring warm (not boiling) water over the outside of the pipe or using warm towels.
• Once thawed, press the reset button to restart the boiler.

Engineer actions:

• Remove and clean the condensate trap, ensuring all debris and sludge are cleared; refill with clean water.
• Check the internal and external condensate pipework for correct fall (slope) and secure fixings; correct any sags or backfalls.
• Insulate external condensate pipework to reduce risk of freezing.