BoilerFaultCodesWorcester Bosch 815 Fault Code
The Worcester Bosch 815 fault code means: your boiler is receiving incorrect temperature readings from a secondary part of your heating system, which may be preventing your home from heating up efficiently.. It appears on 4 Worcester Bosch models in our database.
Technical description: Low loss header temp. sensor faulty
What causes the Worcester Bosch 815 fault?
This fault occurs when the boiler loses a reliable signal from the sensor that monitors the water temperature in your external system piping. It is usually caused by a physical failure of the sensor itself or a loose connection in the wiring that links it back to the main control board. When this happens, the boiler cannot accurately measure how much heat is needed, leading to inefficient operation or a loss of heating.
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 815 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 815 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