BoilerFaultCodesWorcester Bosch D1240 Fault Code
The Worcester Bosch D1240 fault code means: your boiler has detected an electrical fault with the internal sensor that monitors the water returning to the unit, causing it to shut down to prevent damage.. It appears on 2 Worcester Bosch models in our database.
Technical description: The contacts of the boiler return temperature sensor have been short circuited
What causes the Worcester Bosch D1240 fault?
This fault occurs when the electrical signals from the sensor monitoring the return water temperature are disrupted, usually because the sensor has failed or become damaged. The most common reason is that the internal components of the sensor have worn out or a leak has caused moisture to corrode the electrical connections. Because the boiler can no longer accurately measure the water temperature coming back from your radiators, it 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 D1240 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch D1240 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