High Lockout
F.64 on Vaillant ecoMAX Pro 28E

Your boiler has stopped working because its internal computer has detected a fault with its temperature sensors or the main control board.

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 or illogical signals from its temperature sensors. The most common reason is a short circuit in the wiring or a total electronic failure within the main control board, which prevents the boiler from safely monitoring heat levels.

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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