High Lockout
F.0 on Vaillant ecoMAX

Your boiler has lost its connection to the sensor that monitors the temperature of the water 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: – NTC broken – NTC cable broken – Defective connection at NTC – Defective connection at electronics | Flow–NTC cable defective/broken NTC faulty

What causes this fault?

This fault occurs when the boiler's main control board loses the electrical signal from the sensor that monitors hot water leaving the unit. The most common reason is that the sensor itself has internal electrical failure or the wiring connecting it to the circuit board has become loose or damaged over time.

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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