Medium Warning
E321 on Main Eco Compact

Your boiler has detected a problem with the sensor that monitors the temperature of your hot water, meaning your taps may not get as hot as they should or stay consistent.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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

Hot water negative thermistor coefficient (NTC) error

What causes this fault?

This fault occurs when the sensor responsible for measuring the temperature of your hot water fails or sends an incorrect signal to the boiler's control board. The most common reason is that the sensor has physically degraded over time or developed an electrical internal short, preventing it from tracking heat accurately. In some cases, it can also be triggered by loose or corroded wiring connections between the sensor and the main computer.

Engineer required

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

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Related fault codes

E20View →E28View →

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