BoilerFaultCodesWorcester Bosch 8.d Fault Code
Also written as 8D — same fault.
The Worcester Bosch 8.d fault code means: your boiler has detected an internal electronics communication error, which has caused it to stop working for safety.. It appears on 2 Worcester Bosch models in our database.
Technical description: GFA error (not applicable)
What causes the Worcester Bosch 8.d fault?
This fault occurs when the boiler's main control board loses its digital connection with the internal safety sensors or ignition components. The most common reason is a physical failure within the printed circuit board's circuitry or a loose connection in the internal wiring loom that prevents data from flowing correctly.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Worcester Bosch models that show the 8.d fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 8.d 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