High Lockout
F.11 on Vaillant ecoTEC

Your boiler has detected an electrical fault with the sensor that monitors water returning from your radiators, 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

Return NTC short circuit

What causes this fault?

This fault occurs when the electrical connection within the return pipe sensor breaks down, creating a 'short circuit' that sends an incorrect signal to the boiler's computer. The most common reason is internal wear and tear of the sensor itself, though it can also be triggered by water leaking onto the electrical cables or a fault in 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.10View →F.20View →

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