Low
E740 on Navien NCB CE

Your boiler has lost the connection to the thermometer installed outside your home, so it cannot automatically adjust your heating based on the current weather.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Outdoor sensor error

From this model's manual
Verified against the Navien Ncb H installation & service manual, page 78.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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