High Lockout
F.11 on Vaillant ecoTEC exclusive

Your boiler has stopped working because it cannot correctly read the temperature of the water returning to the unit due to an electrical connection issue.

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 in return temperature sensor: Sensor plug has mass short to the casing, short-circuit in wiring loom, sensor faulty

What causes this fault?

This fault occurs when the boiler's control board detects an incorrect electrical signal from the sensor that monitors the temperature of the water coming back from your radiators. The most common reason is that the sensor itself has developed an internal electrical failure or the wiring connecting it to the main board has become trapped, damaged, or wet.

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.01View →F.10View →

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