High Lockout
F.67 on Vaillant Thermocompact

Your boiler's internal computer has encountered a communication error or hardware failure and cannot operate 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

Electronic fault | Electronics defect

What causes this fault?

This fault occurs when the boiler's main control board fails to verify the flame signal or encounters an internal processing error. It is essentially a communication breakdown between the electronic 'brain' and the ignition system, often caused by worn-out components or moisture damage on the circuitry.

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.61View →F.62View →F.63View →F.65View →

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