BoilerFaultCodesWorcester Bosch 9.3 Fault Code
Also written as 93 — same fault.
The Worcester Bosch 9.3 fault code means: your boiler’s internal computer has encountered a memory error and cannot safely operate the heater.. It appears on 5 Worcester Bosch models in our database.
Technical description: GFA-Asic-error
What causes the Worcester Bosch 9.3 fault?
This fault occurs when the boiler's main control board experiences an internal memory failure, meaning it can no longer communicate with the safety software. It is typically caused by a microchip hardware failure or an electrical surge that has corrupted the internal data. Because the computer can no longer guarantee the boiler is running safely, it shuts down the entire system as a precaution.
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 9.3 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 9.3 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