BoilerFaultCodesWorcester Bosch Fault 01 / 201 Fault Code
Also written as FAULT01201 — same fault.
The Worcester Bosch Fault 01 / 201 fault code means: your boiler's internal computer is having trouble communicating with an external control or smart thermostat connected to it.. It appears on 1 Worcester Bosch model in our database.
Technical description: BUS communication fault: Incorrect BUS subscriber connected.
What causes the Worcester Bosch Fault 01 / 201 fault?
This fault occurs when the boiler's main computer chip loses its ability to 'speak' to your wall thermostat or smart controller. It is usually caused by a loose connection in the wiring, a faulty circuit board, or an incompatible smart hub being plugged into the system. Essentially, the boiler has received a signal it doesn't understand and shuts down 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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Gas Safe Register →Worcester Bosch models that show the Fault 01 / 201 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Fault 01 / 201 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