Boiler shows A1 and stops, often associated with low or no water pressure.

Safety first: Ensure the boiler is cool before repressurising. Do not exceed 2.0 bar when cold.

• Check pressure gauge: If the gauge reads below 1.0 bar, repressurise using the filling loop or Worcester Bosch keyless filling link according to the user manual.
• Look for leaks: Inspect visible pipework, radiators, and the boiler underside for signs of water leaks. If a leak is found, isolate and call an engineer.
• Reset the boiler: Once pressure is restored to 1.0–1.5 bar, reset the boiler and check operation.
• Engineer checks: If pressure drops repeatedly, an engineer should check the expansion vessel charge, pressure relief valve, and system for hidden leaks.