How much does it cost to fix Navien error code E278?

Typical repair cost for the Navien E278 fault is £120-200 including labour.

E278 High

Navien E278 Fault Code

Q: What does the Navien E278 fault code mean?

Your boiler is having trouble measuring its own internal temperature, so it has shut down to prevent it from getting too hot or cold.

The Navien E278 fault code means: your boiler is having trouble measuring its own internal temperature, so it has shut down to prevent it from getting too hot or cold.. It appears on 4 Navien models in our database.

Technical description: Abnormal operation: system supply thermistor

Typical repair cost £120-200 (including labour)

Engineer required

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

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Navien models that show the E278 fault code

Click a model for the full fault code list and model-specific repair notes.

NCB 28 HE Repair: £120-200
NCB 35 HE Repair: £120-200
NCB 40 HE Repair: £120-200
NCB H Repair: £120-200

Source

Navien E278 fault code information on this page is sourced and cross-checked against the official Navien service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026