High
F.84 on Vaillant ecoFIT Pure 412

Your boiler has detected that the water temperature is significantly different between the input and output pipes, making it unsure if it is operating safely and effectively.

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

Flow/return temperature sensor difference fault

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.83View →F.22View →

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