BoilerFaultCodesWorcester Bosch 3.C Fault Code
Also written as 3C — same fault.
The Worcester Bosch 3.C fault code means: your boiler is heating up too quickly and has paused itself to prevent over-heating, which often suggests there is a problem with the water circulating through the system.. It appears on 1 Worcester Bosch model in our database.
Technical description: Anti-cycle flow temperature differential
What causes the Worcester Bosch 3.C fault?
This fault occurs when the boiler detects that the water inside the heat exchanger is getting hot much faster than it can be moved around your radiators. The most common reason is a blockage or a failing pump that is preventing the water from circulating properly, causing the heat to build up to unsafe levels within the unit. It can also be caused by air trapped in the system or closed radiator valves stopping the flow of water.
This issue often appears when you first turn the heating back on in autumn, as internal pump parts can seize or sludge can settle during the summer months of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure your system pressure is between 1 and 1.5 bar on the gaugeBleed all radiators to remove trapped air
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Gas Safe Register →Worcester Bosch models that show the 3.C fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 3.C 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