BoilerFaultCodesWorcester Bosch 9U Fault Code
The Worcester Bosch 9U fault code means: your boiler has stopped working because the internal fan is not spinning fast enough to safely clear waste gases from the system.. It appears on 6 Worcester Bosch models in our database.
Technical description: Fan speed too low. Fan harness and connections.
What causes the Worcester Bosch 9U fault?
This fault occurs when the boiler's control system detects that the fan is not rotating at the required speed to safely expel exhaust gases. The most common reasons are a build-up of debris within the fan's bearings, a loose connection in the wiring, or a failing motor that can no longer reach its target velocity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Search the official register for a qualified engineer in your area.
Gas Safe Register →Worcester Bosch models that show the 9U fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 9U 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