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
The same code number can mean something different on another series — make sure you're reading the page for your exact unit:
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: