E445 High

Navien E445 Fault Code

The Navien E445 fault code means: your boiler is having trouble managing the flow of water between your heating system and your hot water taps, which may cause your heating or hot water to stop working properly.. It appears on 3 Navien models 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: Abnormal operation: Bypass mixing valve
Typical repair cost £200-350 (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 E445 fault code

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

Source

Navien E445 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