BoilerFaultCodesWorcester Bosch 9U233 Fault Code
The Worcester Bosch 9U233 fault code means: your boiler's internal computer memory chip is having trouble communicating, which has caused the system to shut down for safety.. It appears on 3 Worcester Bosch models in our database.
Technical description: Heat Control Module (HCM) error – problem with code plug
What causes the Worcester Bosch 9U233 fault?
This fault occurs when the boiler's main control board loses its connection to the code plug, which acts like a memory chip containing the unit's specific settings. The most common reason is a physical failure of the chip itself or a loose connection on the circuit board caused by years of vibration and thermal expansion. Because the boiler no longer knows its own safety parameters, it shuts down immediately to prevent damage.
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 9U233 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 9U233 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