High Lockout
F.0 on Vaillant ecoTEC Plus 65

Your boiler has stopped working because it cannot accurately measure the temperature of the water leaving the unit due to a sensor or wiring connection fault.

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 open circuit. NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics

What causes this fault?

This fault occurs when the boiler's control system loses the signal from the sensor that monitors the temperature of the water flowing out to your radiators. The most common reason is that the sensor itself has failed internally or the electrical wiring connecting it to the main control board has become loose or damaged. Without this vital temperature data, the boiler shuts down as a safety precaution 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.1View →F.10View →F.11View →

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