How much does it cost to fix Baxi error code E321?

Typical repair cost for the Baxi E321 fault is £100-£160 including labour.

E321 Medium

Baxi E321 Fault Code

Q: What does the Baxi E321 fault code mean?

Your boiler has a faulty temperature sensor responsible for tracking the heat of your tap water, which usually results in inconsistent or no hot water.

The Baxi E321 fault code means: your boiler has a faulty temperature sensor responsible for tracking the heat of your tap water, which usually results in inconsistent or no hot water.. It appears on 24 Baxi models in our database.

Technical description: Hot water negative temperature coefficient (NTC) fault.

What causes the Baxi E321 fault?

This fault occurs when the sensor responsible for measuring the temperature of your hot water fails or sends an incorrect signal to the main control board. The most common reason is that the internal components of the sensor have degraded over time or developed a short circuit, meaning the boiler can no longer safely determine how hot the water is. Occasionally, this can also be caused by loose or damaged wiring connecting the sensor to the boiler's computer.

Typical repair cost £100-£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 E321 fault code

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

Source

Baxi E321 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