High Lockout
70 on Alpha E-Tec, E-Tec Plus, Evoke

Your boiler has detected a communication error between its internal temperature sensors, which means it cannot safely monitor the water temperature and has shut down as a precaution.

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

Return/flow sensorExchange from possible wiring fault

What causes this fault?

This fault occurs when the boiler's control board receives conflicting or missing data from the internal sensors that monitor water temperature. The most common reason is a physical failure of the thermistor sensors themselves or a loose connection in the wiring harness that links them to the main computer. Because the boiler can no longer verify if the water is at a safe temperature, it shuts down to prevent overheating.

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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