Low
E740-2 on Navien NCB CE

Your boiler is receiving an incorrect signal from the optional outdoor weather sensor because of a wiring short, though your heating and hot water will still work.

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 temperature sensor short error (appears only when the outdoor reset is enabled).

From this model's manual
Verified against the Navien/Navien Ncb Ce installation & service manual.
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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Related fault codes

E740-1View →E740-3View →

All 95 fault codes on the NCB CE

Seeing a different code? Every code this model can display, in one place.

001003004012012E016016E030046047060109110110E205218302352353407421515517594615740782E.782E001E003E004E012E016E030E046E047E047-1E047-2E060E060-1E060-2E060-3E109E109-0E110E110-1E110-2E110-3E127E205E205-1E205-2E218E218-1E218-2E302E302-0E351E352E352-0E353E353-1E353-2E407E407-1E407-2E421E421-1E421-2E439E515E515-1-7E515-8E515-9E515-10E515-11-12E515-13-14E517E517-0E594E594-0E615E615-0E615-1E615-2E615-3-14E615-15-16E740E740-1E782E782-0E783E787TEC

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