High Lockout
F.63 on Vaillant Thermocompact

Your boiler has detected an internal electrical communication error, which means the main control board is likely faulty and cannot manage the heating process 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

EMC fault | EMC or electronics defect

What causes this fault?

This fault occurs when the boiler's central brain, the printed circuit board, suffers an internal memory or electrical failure. It is often caused by aged electrical components wearing out over time or a sudden power surge that damages the delicate circuitry. Because the board can no longer safely coordinate the boiler's functions, it shuts down the system.

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.64View →F.67View →

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