Navien NPE-A / NPE-S Code E515
PCB fault. The control board has reported a fault in itself. Navien gives one owner-facing check and it is worth doing before accepting a board replacement: make sure the electrical cord is properly grounded. A grounding problem can present as a board fault.
Call a proThe verdict
Call a licensed plumber
The most expensive single part on the unit after the heat exchanger, so it is worth ruling out the free cause first. Navien names grounding for a reason.
Typical cost: $150–$1,100
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
- Confirm the heater is plugged into a properly grounded outlet, and that nothing about its power supply has changed recently.
- Before agreeing to a board replacement, ask whether grounding was checked — it is the manual's own instruction for this code.
- Book a licensed professional.
Code E515 on other Navien series
Other Navien series report code E515 under the same fault name, but each manual is transcribed separately and they do not read alike: