BoilerFaultCodesWorcester Bosch Fault 02 / 100 Fault Code
Also written as FAULT02100 — same fault.
The Worcester Bosch Fault 02 / 100 fault code means: your boiler's main control unit is having a communication breakdown with its internal safety components, meaning it cannot operate safely and has shut down.. It appears on 1 Worcester Bosch model in our database.
Technical description: Internal fault: ISM not responding.
What causes the Worcester Bosch Fault 02 / 100 fault?
This fault occurs when the boiler's central brain loses its connection with the internal safety module that monitors the flame. The most common cause is an electronic failure within the internal circuitry or a loose connection on the main control board. Because the boiler can no longer verify that it is burning gas safely, it shuts down instantly as a protective measure.
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 / 100 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Fault 02 / 100 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