Medium
740 on Navien NCB H

Your boiler's external temperature sensor is reporting an issue, which may cause it to run inefficiently or struggle to heat your home correctly.

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

740Error

Engineer required

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

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