High Lockout
F.0 on Vaillant ecoTEC exclusive

Your boiler has lost its connection to the sensor that measures the water temperature as it leaves the unit, meaning it cannot safely judge how much heat to provide.

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

Interruption feed temperature sensor (NTC): NTC faulty, NTC cable faulty, faulty plug connection on NTC, faulty plug connection on the electronics

What causes this fault?

This fault occurs when the boiler's central brain loses communication with the temperature sensor on the main pipe. The most common reason is a physical breakage in the internal wiring or the sensor itself failing due to age and constant heat cycles. Without this signal, the boiler shuts down as a safety precaution because it cannot monitor if the water is becoming dangerously hot.

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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