High Lockout
F031 on Intergas Xtreme / Xclusive

Your boiler has stopped working because one of its internal heat sensors is reporting a fault, meaning the system can no longer safely monitor the water temperature.

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 S1

What causes this fault?

This fault occurs when the boiler's main flow sensor sends an incorrect or interrupted signal to the control board, preventing the system from knowing if it is safe to fire. The most common cause is a physical failure of the sensor’s internal components, though it can also be triggered by loose or corroded wiring connections that break the electrical circuit.

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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