BoilerFaultCodesWorcester Bosch 3.b Fault Code
Also written as 3B — same fault.
The Worcester Bosch 3.b fault code means: your boiler is taking a short, programmed rest to prevent itself from switching on and off too frequently, which helps protect the internal components from unnecessary wear.. It appears on 1 Worcester Bosch model in our database.
Technical description: Anti-cycle time
What causes the Worcester Bosch 3.b fault?
This occurs when your boiler reaches its target temperature and needs to pause briefly before firing up again. It is a protective measure triggered when the heat in the system hasn't dissipated yet, preventing the burner from 'short-cycling' and wasting energy. This often happens if your radiators are already hot or if the boiler's heat output is temporarily higher than what your radiators can currently handle.
This code is more common during the autumn and spring when the weather is milder and your home doesn't require the boiler to run at full power constantly.
DIY fix possible
Wait for 15 to 30 minutes as the boiler will likely restart automatically once the cooling period ends.Check that your room thermostat is turned up higher than the current room temperature.Ensure all radiator valves are fully open to allow heat to move away from the boiler more quickly.
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Gas Safe Register →Worcester Bosch models that show the 3.b fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 3.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