High Lockout
F04 on Intergas Rapid 25

Your boiler has stopped working because it cannot detect a signal from the internal sensor that monitors the temperature of your hot water.

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

S2 sensor open circuit

What causes this fault?

This fault occurs when the boiler's control board loses communication with the sensor responsible for monitoring your hot water temperature. The most common cause is the sensor itself failing internally, but it can also be triggered by a loose connection or damaged wiring between the sensor and the main circuit board.

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

F01View →F02View →F03View →

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