BoilerFaultCodesWorcester Bosch 1-A2 Fault Code
Also written as 1A2 — same fault.
The Worcester Bosch 1-A2 fault code means: your boiler has detected an internal communication error or a software glitch that is preventing the system from starting up safely.. It appears on 3 Worcester Bosch models in our database.
Technical description: Current fault: Fault code (table 10.1.2)
What causes the Worcester Bosch 1-A2 fault?
This fault occurs when the boiler's main control board loses touch with the internal components it needs to manage, often due to a breakdown in electronic communication. The most common reason is a malfunction within the Printed Circuit Board itself or a loose connection in the wiring harness that carries signals throughout the unit. Because the 'brain' of the boiler can no longer verify that it is safe to operate, it stops the system from firing up.
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 1-A2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Worcester Bosch 1-A2 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