How much does it cost to fix Baxi error code E.04 – .05?

Typical repair cost for the Baxi E.04 – .05 fault is £90-180 including labour.

E.04 – .05 High

Baxi E.04 – .05 Fault Code

Q: What does the Baxi E.04 – .05 fault code mean?

Your boiler has detected a problem with a safety sensor that monitors the temperature of the exhaust gases, causing the system to lock out.

Also written as E0405 — same fault.

The Baxi E.04 – .05 fault code means: your boiler has detected a problem with a safety sensor that monitors the temperature of the exhaust gases, causing the system to lock out.. It appears on 24 Baxi models in our database.

Technical description: Permanent fault. Flue temperature sensor short-circuited, sensor not or badly connected, bad connection or sensor fault.

What causes the Baxi E.04 – .05 fault?

This fault occurs when the boiler's safety system detects an irregular electrical signal from the sensor that monitors the heat of the exhaust gases. The most common reason is that the sensor has developed an internal electrical short or the wiring connecting it to the main control board has become loose or damaged. In some cases, it can be triggered if the heat exchanger is extremely dirty, causing exhaust temperatures to exceed safe limits.

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 E.04 – .05 fault code

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

Source

Baxi E.04 – .05 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 27 April 2026