High Lockout
F.0 on Vaillant ecoTEC

Your boiler has lost its connection to the sensor that monitors the temperature of the water leaving the unit, causing it to stop running as a safety precaution.

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

What causes this fault?

This fault occurs when the boiler's internal computer can no longer detect a signal from the sensor that monitors hot water leaving the unit. 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. Because the boiler cannot safely verify 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.1View →F.10View →F.22View →

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