BoilerFaultCodesWorcester Bosch A5 Fault Code
The Worcester Bosch A5 fault code means: your boiler has detected an electrical communication problem with its internal control system which is preventing it from firing up.. It appears on 3 Worcester Bosch models in our database.
Technical description: DC supply pipe
What causes the Worcester Bosch A5 fault?
This fault occurs when the boiler's internal computer loses the ability to communicate with the sensors that monitor the gas and water flow. It is usually caused by a physical break in the internal wiring or a failure in the electronic components on the main control board. Because the boiler can no longer verify that it is safe to operate, it shuts down immediately as a safety precaution.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Worcester Bosch models that show the A5 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch A5 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.
- Worcester Bosch CDi Highflow manual (PDF)
- Worcester Bosch Highflow CDi manual (PDF)
- Worcester Bosch WR325 RSF manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026