305 High

Navien 305 Fault Code

The Navien 305 fault code means: your boiler's internal computer is unable to verify the connection to a key component, causing the system to stop working as a precaution.. It appears on 1 Navien model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: 305:Eng under current: Engine connectivity test failed. This test lasts for at most one minute following the start of engine operation. Measured current must be greater than 100 mA for 10 seconds to pass the test.
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 305 fault code

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

Source

Navien 305 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