High Lockout
F.01 on Vaillant ecoMAX Pro 28E

Your boiler has stopped working because a sensor that monitors the temperature of the water returning to the unit has disconnected or failed.

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

Return NTC open circuit

What causes this fault?

This fault occurs when the boiler's internal computer loses communication with the sensor that monitors the temperature of the water coming back from your radiators. The most common reason is that the sensor has physically failed or a wire has shaken loose, meaning the boiler can no longer safely regulate the heating process.

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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