BoilerFaultCodesWorcester Bosch 9.d Fault Code
Also written as 9D — same fault.
The Worcester Bosch 9.d fault code means: your boiler is failing to start because the internal fan is not spinning at the speed required to clear waste gases.. It appears on 1 Worcester Bosch model in our database.
Technical description: Start fan speed
What causes the Worcester Bosch 9.d fault?
This fault occurs when the boiler's control system attempts to start the fan but detects that it isn't reaching the necessary speed to safely vent exhaust gases. The most common reason is a mechanical failure within the fan motor or a communication error where the main circuit board cannot correctly read the fan's rotation speed.
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 9.d fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 9.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