High Lockout
F.64 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler has detected a communication problem between its internal sensors or a fault in its main control board, causing the system to shut down for safety.

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

Electronics / NTC error

What causes this fault?

This fault occurs when the boiler's internal computer receives conflicting information from its temperature sensors or detects a short circuit in the wiring. The most common reason is that either the flow or return sensors have failed, or the main circuit board can no longer accurately process the signals it is receiving.

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 →F.67View →

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