High Lockout
F.0 on Vaillant ecoMAX 618

Your boiler has lost connection with its main internal temperature sensor, meaning it cannot safely tell how hot the water is and has shut down as a 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: NTC broken, NTC cable broken, Defective connection at NTC, Defective connection at electronics | Cause: Flow–NTC cable defective/broken NTC faulty

What causes this fault?

This fault occurs when the boiler's internal computer can no longer detect a signal from the sensor that monitors water temperature. The most common reason is that the sensor itself has simply worn out over time, though it can also be caused by a loose connection or damaged wiring inside the unit.

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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