A-b2 Medium

Worcester Bosch A-b2 Fault Code

Also written as AB2 — same fault.

The Worcester Bosch A-b2 fault code means: your boiler has detected an issue with how quickly hot water is moving through the system, which may result in inconsistent water temperatures.. It appears on 1 Worcester Bosch model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: DHW flow rate: Hot water flow rate

What causes the Worcester Bosch A-b2 fault?

This fault occurs when the boiler's internal sensors detect an unusual or inconsistent flow of water when you turn on a hot tap. It is usually caused by a physical blockage in the flow turbine, a build-up of limescale within the heat exchanger, or a communication error between the electronic sensor boards.

Typical repair cost £90-180 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the A-b2 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch A-b2 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026