High Lockout
F.10 on Vaillant ecoTEC Plus 65

Your boiler has detected an electrical fault with the internal sensor that monitors the water temperature leaving the unit, causing it 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

Flow NTC short circuit. NTC defective, short circuit in cable harness, cable/casing short cut

What causes this fault?

This fault occurs when the electrical connection to the flow sensor is interrupted, usually by a short circuit in the sensor itself or the internal wiring. This is often caused by moisture ingress from a small leak or natural wear and tear to the electrical components over time. Because the boiler can no longer safely track how hot the water is, it shuts down to prevent overheating.

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.00View →F.11View →F.20View →

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