High Lockout
F.25 on Vaillant ecoTEC exclusive

Your boiler has detected an internal electrical connection issue that is preventing it from running safely.

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

Safetyswitch-off:Fluetemp.toohigh | Breakinplugconnectionforoptionalfluegassafetycut-out(SCO), breakincableharness

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with its safety sensors due to a break in the electrical circuit. It is typically caused by a loose connection, a damaged plug on the wiring loom, or a failure within the main control board itself.

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

F.22View →F.23View →F.24View →

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