BoilerFaultCodesWorcester Bosch 3.F Fault Code
Also written as 3F — same fault.
The Worcester Bosch 3.F fault code means: your boiler has detected an error while turning off the burner after you used your hot water taps, which may prevent it from firing up again.. It appears on 1 Worcester Bosch model in our database.
Technical description: Burner off after DHW demand (hot water - combi only)
What causes the Worcester Bosch 3.F fault?
This fault occurs when the boiler's internal computer detects that the burner flame is still present or being reported after you have finished using your hot water. It is usually caused by a communication error on the main circuit board or a mechanical part like the diverter valve failing to move into the correct position. In some cases, an external sensor may also be sending incorrect electrical signals that confuse the boiler's shutdown sequence.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Worcester Bosch models that show the 3.F fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 3.F 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