High
F.12 on Vaillant ecoFIT Pure 825

Your boiler is struggling to detect the temperature of your hot water due to a wiring issue or a faulty sensor, so it has stopped heating to prevent potential damage.

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: Cylinder temperature sensor

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.13View →

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