04 Medium

Baxi 04 Fault Code

The Baxi 04 fault code means: your boiler has detected an issue with the sensor that monitors your hot water temperature, meaning your water might not get hot enough or could be too hot.. It appears on 3 Baxi models 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 Temperature
Typical repair cost £90-180 (including labour)

Engineer required

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

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Baxi models that show the 04 fault code

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

Source

Baxi 04 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026