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