2964 B High

Worcester Bosch 2964 B Fault Code

Also written as 2964B — same fault.

The Worcester Bosch 2964 B fault code means: your boiler has detected that water is not moving through its internal heating unit fast enough, which can cause the system to overheat and shut down.. It appears on 13 Worcester Bosch models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Flow rate in heat exchanger is too low

What causes the Worcester Bosch 2964 B fault?

This fault occurs when water is unable to circulate through the boiler's main heat exchanger at the required speed to safely carry heat away. The most common reasons are a failing internal pump, a build-up of sludge or debris blocking the pipework, or a secondary heat exchanger that has become restricted over time.

This issue often comes to light during the first cold spell of autumn when the heating is turned back on and the pump or system is pushed to work harder after sitting idle all summer.

Typical repair cost £120-£450 (including labour)

DIY fix possible

Check that your system pressure is between 1 and 1.5 bar on the front displayEnsure all radiator valves are fully open to allow water to circulateInspect the magnetic system filter, if fitted, to see if it needs cleaning

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Worcester Bosch models that show the 2964 B fault code

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

Source

Worcester Bosch 2964 B 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