BoilerFaultCodesWorcester Bosch 108 Fault Code
The Worcester Bosch 108 fault code means: your boiler has lost water pressure, which is preventing it from firing up to provide heat or hot water.. It appears on 1 Worcester Bosch model in our database.
Technical description: 12kW NG with external diverter valve code plug
DIY fix possible
Locate the filling loop (usually a silver braided hose under the boiler).Open the small black valves slowly until you hear water entering.Close the valves when the pressure gauge reaches between 1 and 1.5 bar.
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Gas Safe Register →Worcester Bosch models that show the 108 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 108 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