BoilerFaultCodesWorcester Bosch 9A Fault Code
The Worcester Bosch 9A fault code means: your boiler has stopped working because the internal pump that moves water around your heating system has become stuck or failed.. It appears on 3 Worcester Bosch models in our database.
Technical description: The display shows alternatively the CH flow temperature and 9A. The pump is blocked. See error E9.
What causes the Worcester Bosch 9A fault?
This fault occurs when the boiler's internal pump is unable to spin, preventing hot water from leaving the unit. The most common reason is a build-up of black iron oxide sludge that physically jams the moving parts, or an electrical failure within the pump motor itself. Without a working pump, the boiler shuts down immediately to prevent the internal heat exchanger from overheating.
This fault is frequently seen at the start of autumn when heating systems are turned back on after being idle all summer, allowing settled debris to seize the pump.
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 9A fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 9A 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