4-A4 Low

Worcester Bosch 4-A4 Fault Code

Also written as 4A4 — same fault.

The Worcester Bosch 4-A4 fault code means: your boiler is simply letting you know that it is due for its routine annual service based on how long it has been running.. It appears on 1 Worcester Bosch model in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Service display / Inspection interval according to hours run: 0: switched off, 1: acc. to hours run, 3: acc. to elapsed time.
Typical repair cost £80-120 (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 4-A4 fault code

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

Source

Worcester Bosch 4-A4 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