BoilerFaultCodesWorcester Bosch D4271 Fault Code
The Worcester Bosch D4271 fault code means: your boiler has detected that the water is heating up too quickly or isn't circulating properly, causing it to shut down to prevent overheating.. It appears on 2 Worcester Bosch models in our database.
Technical description: Actual temperature differential between flow and safety temperature sensor is too high
What causes the Worcester Bosch D4271 fault?
This fault occurs when water cannot move through the boiler fast enough to carry heat away, causing a rapid and dangerous rise in temperature. The most common reasons are a failed internal pump that has stopped spinning or a blockage caused by a buildup of sludge and debris within the main heat exchanger. In some cases, it may simply be caused by air trapped in the system or sensors that are providing incorrect temperature readings to the control board.
This fault often appears when the heating is first turned on after summer, as the internal pump can seize up during long periods of inactivity.
DIY fix possible
Check that your radiator valves and any isolation valves are fully openEnsure your system pressure is topped up to between 1 and 1.5 barBleed your radiators to remove any trapped air that might be blocking circulation
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Gas Safe Register →Worcester Bosch models that show the D4271 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch D4271 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