BoilerFaultCodesWorcester Bosch Fault 40 101 Fault Code
Also written as FAULT40101 — same fault.
The Worcester Bosch Fault 40 101 fault code means: your boiler has detected an electrical fault with its main temperature sensor, causing the system to shut down safely to prevent overheating.. It appears on 2 Worcester Bosch models in our database.
Technical description: Short circuit on the sensor lead (T1). Temperature sensor T1 on collector group 1 faulty.
What causes the Worcester Bosch Fault 40 101 fault?
This fault occurs when the boiler's main internal thermometer, which monitors water temperature, fails to send a correct electrical signal to the control board. The most common reason is that the sensor has developed an internal electrical short or the protective coating on the thin wires connecting it has worn through or vibrated loose. Because the boiler can no longer accurately tell how hot the water is, 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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Gas Safe Register →Worcester Bosch models that show the Fault 40 101 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Fault 40 101 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