E40 High

Baxi E40 Fault Code

The Baxi E40 fault code means: your boiler has detected an issue with the sensor that monitors the temperature of the water returning from your radiators.. It appears on 24 Baxi models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Central heating return negative temperature coefficient (NTC) thermostat fault.

What causes the Baxi E40 fault?

This fault occurs when the boiler's internal computer receives an illogical or missing signal from the sensor that monitors water returning from your radiators. The most common reason is that the sensor has physically failed or developed a chemical build-up, but it can also be caused by damaged internal wiring or a loose connection.

This fault is more common when the heating is first turned on after summer, as the sudden change in temperature can cause aging sensors to fail.

Typical repair cost £90-160 (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 E40 fault code

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

Source

Baxi E40 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