High Lockout
F.10 on Vaillant Thermocompact

Your boiler has detected an electrical fault with the internal temperature sensor that monitors the outward flow of water, causing the system to shut down for safety.

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

Short circuit - flow-NTC (< 130 °C) | NTC- plug shorted to casing NTC defective

What causes this fault?

This fault occurs when the electrical signal from the sensor that monitors the temperature of the water leaving your boiler is interrupted. The most common cause is a failure of the internal thermistor component itself, but it can also be triggered by damaged wiring touching the metal boiler casing or a failure on the main control board.

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.11View →F.20View →

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