BoilerFaultCodesWorcester Bosch 1-A1 Fault Code
Also written as 1A1 — same fault.
The Worcester Bosch 1-A1 fault code means: your boiler is currently stuck in a temporary startup phase and is waiting for everything to be ready before it begins heating.. It appears on 1 Worcester Bosch model in our database.
Technical description: Current status: Status code.
What causes the Worcester Bosch 1-A1 fault?
This code appears when the boiler is performing its internal self-checks and preparing its components before officially starting a heating cycle. It is a normal part of the startup sequence and usually indicates the system is simply waiting for a sensor or fan to reach the correct operating state. If the code stays on the screen, it typically means the control board is waiting for a signal that isn't arriving.
DIY fix possible
Wait 15 minutes to see if the boiler clears the code automaticallyEnsure your thermostat is calling for heat or hot waterRestart the boiler using the power button if the code persists for more than 30 minutes
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Gas Safe Register →Worcester Bosch models that show the 1-A1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1-A1 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