High
Red flashing light on Saunier Duval Themaclassic F25E

Your boiler has detected a general issue and has entered a safety lockout mode.

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

General fault indicator. Reset the boiler by turning the On/Off switch to ( 0 ), waiting five seconds, and turning back to ( I ).

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.

Find a Gas Safe engineer
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Related fault codes

F1View →F4View →

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