Medium
F.91 on Vaillant ecoTEC plus Regular

Your boiler has lost the ability to monitor the temperature of your hot water cylinder because of a faulty connection or sensor.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Shortcircuit:Cylindertemperaturesensor

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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