Navien NPE-A / NPE-S Code E445
Bypass mixing valve fault. The bypass mixing valve — which blends heated water with water routed around the heat exchanger to hold the outlet steady — is not reporting correctly. Navien's instruction is to contact technical support.
Part replacementThe verdict
Replace a part
A moderate part with the cabinet open. Like the water adjustment valve, the symptom is temperature that will not settle rather than a dead unit.
Typical cost: $200–$600
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the NPE-A / NPE-S — not averaged across the brand.
Source: Navien NPE Operation Manual (NPE-A / NPE-S) (p. 16), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
- Book a service call.
Code E445 on other Navien series
Other Navien series report code E445 under the same fault name, but each manual is transcribed separately and they do not read alike:
Don't confuse this with
One other Navien NPE-A / NPE-S code points at a valve too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: