Medium
740 on Navien NCB 40 HE

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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