Worcester Bosch A1 Fault

Worcester Bosch A1 Fault

The Worcester Bosch boiler A1 fault code is indicative of a problem related to water circulation within the system or an issue with the pressure. Specifically, this fault code can signal that the boiler has either lost water pressure or there’s a failure in the pump preventing effective water circulation. Here’s how to understand and potentially address the A1 fault:

Causes of the A1 Fault Code

  1. Low Water Pressure: If the water pressure in your boiler system drops below a certain point, it can trigger the A1 fault code. This drop in pressure can be due to leaks in the system, recently bled radiators, or natural pressure loss over time.
  2. Pump Failure or Blockage: The A1 fault code may also appear if the pump, responsible for circulating water through the heating system, is blocked, failing, or not operating correctly. This could be due to debris in the system or a mechanical failure of the pump itself.

Troubleshooting the A1 Fault Code

  1. Check the Pressure Gauge: First, look at the boiler’s pressure gauge. The normal operating pressure is usually between 1 and 1.5 bar. If the pressure is below 1 bar, the system may need repressurizing.
  2. Repressurize the Boiler: If the pressure is too low, you can try to repressurize the system using the filling loop. The instructions for this should be in your boiler’s manual. Be careful to follow the instructions precisely to avoid overpressurizing the system.
  3. Check for Leaks: Inspect your radiators, pipes, and the boiler for any signs of leaks. Even a small leak can cause a drop in pressure over time. If you find any leaks, you’ll need to have them repaired.
  4. Pump and System Check: If the pressure seems fine and there are no obvious leaks, the issue might be with the pump or a blockage in the system. Listen to see if the pump is running; a lack of noise could indicate a problem. However, diagnosing pump issues or blockages typically requires the expertise of a professional.
  5. Call a Professional: For issues related to the pump or if you’re unable to identify the cause of the low pressure, it’s best to contact a Gas Safe registered engineer. They can diagnose and fix the problem safely and efficiently.
  6. Preventive Maintenance: Regular servicing of your boiler by a qualified professional can help prevent issues like the A1 fault by ensuring the system is properly maintained, the pressure is correct, and the pump is in good working order.


The A1 fault code on a Worcester Bosch boiler points to issues with water pressure or circulation problems. While some causes, like low water pressure, can be addressed by homeowners, others, especially those related to the pump or internal blockages, require professional intervention. Regular maintenance and prompt attention to any signs of leaks or pressure drops can help prevent the recurrence of the A1 fault code.