1-b3 Medium

Worcester Bosch 1-b3 Fault Code

Also written as 1B3 — same fault.

The Worcester Bosch 1-b3 fault code means: your boiler has detected that the hot water is getting too hot, likely due to a sensor measurement issue or a temporary building of heat in the system.. 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: DHW actual temperature: Actual hot water temperature.

What causes the Worcester Bosch 1-b3 fault?

This fault occurs when the boiler detects that the water coming out of your hot taps is reaching an unsafe or unexpectedly high temperature. The most common reason is a faulty temperature sensor (NTC) providing an incorrect reading to the control board, or a small blockage in the heat exchanger that prevents heat from being transferred efficiently.

Typical repair cost £90-180 (including labour)

DIY fix possible

Turn off the hot water tap and wait for the boiler to cool downPress the 'Reset' button on the boiler display panelMonitor the boiler to see if the hot water temperature stabilises

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Worcester Bosch models that show the 1-b3 fault code

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

Source

Worcester Bosch 1-b3 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