BoilerFaultCodesWorcester Bosch Fault 02 / 43 Fault Code
Also written as FAULT0243 — same fault.
The Worcester Bosch Fault 02 / 43 fault code means: your boiler's main control unit is confused because a small internal configuration plug has moved or is failing, causing the system to lock out for safety.. It appears on 1 Worcester Bosch model in our database.
Technical description: Internal fault: Coding switch position has been changed since initialisation phase.
What causes the Worcester Bosch Fault 02 / 43 fault?
This fault occurs when the boiler's main control board loses its unique identity because the small internal configuration chip has either come loose or failed. It is usually caused by physical vibrations over time or electrical interference preventing the board from reading the chip correctly. Because the boiler is no longer sure of its specific model and settings, it shuts down as a vital safety 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 Fault 02 / 43 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Fault 02 / 43 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