High Lockout
F.00 on Vaillant ecoTEC Pro 28

Your boiler has lost connection with its internal thermometer, 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

Interruption: Flow sensor - Flow temperature sensor defective or not connected

What causes this fault?

This fault occurs when the boiler's control board can no longer detect a signal from the sensor that monitors the temperature of the water leaving the unit. The most common cause is a failure of the internal thermistor itself, though it can also be triggered by loose or corroded electrical connections within the boiler's internal wiring.

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.01View →F.10View →F.11View →

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