BoilerFaultCodesWorcester Bosch 2966 Fault Code
The Worcester Bosch 2966 fault code means: your boiler is overheating too quickly because water isn't moving through the system fast enough.. It appears on 5 Worcester Bosch models in our database.
Technical description: Flow temperature rise in heat exchanger too rapid
What causes the Worcester Bosch 2966 fault?
This fault occurs when the water inside the boiler heats up much faster than the system can carry it away, causing the unit to shut down to prevent damage. The most common reasons are a failing internal pump that isn't pushing the water through, or a build-up of sludge and debris that has restricted the narrow channels within the heat exchanger.
This issue often comes to light during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves are fully openEnsure the system pressure is between 1.0 and 1.5 barBleed your radiators to remove any trapped air
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Worcester Bosch models that show the 2966 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 2966 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
- Worcester Bosch Greenstar 1000 manual (PDF)
- Worcester Bosch Greenstar 2000 manual (PDF)
- Worcester Bosch Greenstar 27CDi manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026