High Lockout
F.01 on Vaillant Turbomax Plus 828

Your boiler has stopped working because one of its internal temperature sensors is not communicating correctly with the main control board.

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: NTCbroken; NTCcable broken; Defective connection at NTC Defective connection at electronics | Return-NTC cable defective/broken NTC faulty

What causes this fault?

This fault occurs when the boiler's main control board loses communication with the sensor that monitors the temperature of the water leaving the unit. The most common reasons are an electrical failure within the sensor itself or a break in the wiring caused by vibration, heat exposure, or moisture. Without this data, the boiler shuts down as a safety precaution to prevent overheating.

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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