High
F.84 on Vaillant ecoTEC exclusive

Your boiler is confused because its temperature sensors are detecting heat patterns that do not match the expected flow of water, often caused by the sensors being swapped or losing contact with the pipes.

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

Fault:NTCtemp.diff.implausible Flowandreturntemperaturesensorsreturningimplausiblevalues. – Flowandreturntemperaturesensorshavebeeninverted – Flowandreturntemperaturesensorshavenotbeencorrectlyin- stalled

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.85View →

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