High Lockout
E321 on Baxi Duo-tec Combi

Your boiler has detected a problem with the sensor that monitors hot water temperature, which may mean you have no hot water or the temperature is inconsistent.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Not water thermistor fault

What causes this fault?

This fault occurs when the boiler's control board can no longer read a reliable signal from the sensor that monitors your hot water. The most common reason is that the internal components of the sensor have degraded over time or the electrical connection has become loose or corroded. Because the boiler doesn't know how hot the water is, it stops heating it as a safety precaution to prevent scalding.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

E20View →E28View →E31View →

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