How much does it cost to fix Navien error code 109?

Typical repair cost for the Navien 109 fault is £150-300 including labour.

109 High

Navien 109 Fault Code

Q: What does the Navien 109 fault code mean?

Your boiler has detected an issue with the airflow or exhaust system, meaning it cannot operate safely and has shut itself down.

The Navien 109 fault code means: your boiler has detected an issue with the airflow or exhaust system, meaning it cannot operate safely and has shut itself down.. It appears on 7 Navien models in our database.

Technical description: Error 109

Typical repair cost £150-300 (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 109 fault code

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

NCB Repair: £120-£250
NCB 28 HE Repair: £150-300
NCB 35 HE Repair: £150-300
NCB 40 HE Repair: £150-300
NCB CE Repair: £150-350
NCB H Repair: £150-300
NHB 29 Repair: £150-300

Source

Navien 109 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