4-b1 Low

Worcester Bosch 4-b1 Fault Code

Also written as 4B1 — same fault.

The Worcester Bosch 4-b1 fault code means: your boiler is simply indicating whether its internal weather-monitoring feature is currently turned on or off.. 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: Device-internal weather-compensated control: OFF: not active, ON: active.

DIY fix possible

Locate the boiler's control panelNavigate to the secondary settings menuEnable or disable the 'Weather Compensation' setting based on your preference

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Worcester Bosch models that show the 4-b1 fault code

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

Source

Worcester Bosch 4-b1 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