High Lockout
21 on Intergas Combi Compact HRE SB

Your boiler has detected a problem with the temperature sensor that monitors the water returning to the unit, causing it to stop running for safety.

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

Sensor fault S2

What causes this fault?

This fault occurs when the boiler's internal computer stops receiving a reliable temperature reading from the sensor on the return pipe. It is usually caused by the sensor itself failing, or a loose connection in the wiring that prevents the signal from reaching the control board. For safety, the boiler shuts down because it can no longer monitor if the water returning from your radiators is at a safe temperature.

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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