BoilerFaultCodesWorcester Bosch Fault 40 102 Fault Code
Also written as FAULT40102 — same fault.
The Worcester Bosch Fault 40 102 fault code means: your boiler has lost connection with a temperature sensor, which means it cannot accurately monitor the water temperature to operate safely.. It appears on 2 Worcester Bosch models in our database.
Technical description: Break in the sensor lead (T1). Temperature sensor T1 on collector group 1 faulty.
What causes the Worcester Bosch Fault 40 102 fault?
This fault occurs when the boiler's control board loses communication with the flow temperature sensor, which monitors the heat of the water leaving the unit. The most common cause is either a physical break in the internal wiring or a failure of the sensor's internal components due to age and heat stress. Because the boiler no longer knows how hot the water is, it shuts down as a safety precaution to prevent overheating.
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 40 102 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch Fault 40 102 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