How much does it cost to fix Worcester Bosch error code D4?

Typical repair cost for the Worcester Bosch D4 fault is £150-300 including labour.

D4 High

Worcester Bosch D4 Fault Code

Q: What does the Worcester Bosch D4 fault code mean?

Your boiler has detected that the water temperature is changing too quickly or unevenly between different parts of the system, so it has safely shut itself down as a precaution.

The Worcester Bosch D4 fault code means: your boiler has detected that the water temperature is changing too quickly or unevenly between different parts of the system, so it has safely shut itself down as a precaution.. It appears on 3 Worcester Bosch models in our database.

Technical description: Temperature difference between flow and safety sensors exceeds limit

Typical repair cost £150-300 (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 D4 fault code

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

Source

Worcester Bosch D4 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