High Lockout
F6 on Vaillant ecoMAX Pro 28E

Your boiler has lost its ability to measure the temperature of the water leaving the unit, usually due to a faulty sensor or a wiring issue.

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

Central heating flow NTC fault

What causes this fault?

This fault occurs when the boiler's internal computer can no longer detect a reliable signal from the sensor that monitors the temperature of the water being sent to your radiators. The most common reason is that the sensor itself has failed internally due to age, or the electrical connection between the sensor and the main control board has become loose or damaged.

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

F1View →F10View →F11View →

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