BoilerFaultCodesWorcester Bosch 1.A Fault Code
Also written as 1A — same fault.
The Worcester Bosch 1.A fault code means: your boiler is temporarily running at its maximum power level, which is usually a normal setting used by engineers during testing or after a reset.. It appears on 1 Worcester Bosch model in our database.
Technical description: Max. output (heating)
What causes the Worcester Bosch 1.A fault?
This status occurs when the boiler has been manually put into its maximum power mode, often through the service buttons on the front panel. It typically happens after a reset or when an engineer is calibrating the gas valve to ensure the unit can handle peak demand. In most cases, it is not a breakdown but a configuration setting that needs to be toggled off to return to normal operation.
DIY fix possible
Check if the chimney sweep or service mode button has been pressedPress the Reset button to return the boiler to normal operationObserve the display to see if the code clears automatically after a few minutes
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Gas Safe Register →Worcester Bosch models that show the 1.A fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1.A 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