65 Low

Navien 65 Fault Code

The Navien 65 fault code means: your boiler is having trouble reading the temperature in the second heating zone controlled by an external wall sensor.. It appears on 1 Navien model in our database.

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.

Technical description: Room sensor 2: Fault room temp sensor hc2
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 65 fault code

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

Source

Navien 65 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 7 July 2026