5-A3 Medium

Worcester Bosch 5-A3 Fault Code

Also written as 5A3 — same fault.

The Worcester Bosch 5-A3 fault code means: your boiler is struggling to run at its lowest power setting, which can cause it to shut down for safety while heating your home or water.. It appears on 1 Worcester Bosch model in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Minimum boiler output (heating and DHW).
Typical repair cost £120-280 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Worcester Bosch models that show the 5-A3 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch 5-A3 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