How much does it cost to fix Vaillant error code lock out?

Typical repair cost for the Vaillant lock out fault is £120-250 including labour.

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Vaillant lock out Fault Code

Q: What does the Vaillant lock out fault code mean?

Your boiler has stopped working because it cannot detect a flame, most likely because the gas supply is interrupted or there is air trapped in the pipes.

Also written as LOCKOUT — same fault.

The Vaillant lock out fault code means: your boiler has stopped working because it cannot detect a flame, most likely because the gas supply is interrupted or there is air trapped in the pipes.. It appears on 2 Vaillant models in our database.

Technical description: The 'lock out' indicator will illuminate. This usually means that the gas supply is turned off, or is not purged of air.

Typical repair cost £120-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the lock out fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant lock out fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026