High Lockout
F.01 on Vaillant ecoTEC Pro 28

Your boiler has stopped working because it cannot communicate with the sensor that monitors the temperature of the water returning from your radiators.

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: Return sensor - Return temperature sensor defective or not connected

What causes this fault?

This fault occurs when the boiler's main control board loses its electrical connection to the sensor that monitors water coming back from your radiators. The most common reason is that the sensor itself has developed an internal electrical fault, or the thin wires connecting it to the system have 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.00View →F.10View →F.11View →

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