Navien E515: PCB Error
There's no obvious plumbing or gas problem, but the unit stops responding and E515 shows on the display — a fault on the printed circuit board that runs the whole system, rather than any single sensor or valve.
Applies to: Navien NPE, NCB, and NHB tankless and combi/condensing water heaters
What it means
PCB Error — the main printed circuit board has detected an internal malfunction. This is a catch-all code for a problem the board finds within itself, which is why the fix path here is narrower than for a code that names one specific sensor or valve.
Most common causes
- Control board fault or component failure
- Power surge damage
- Firmware/communication glitch
What you can safely check yourself
- Power-cycle the unit (unplug or shut off power for about a minute, then restore it) and see if the code clears
When to call a professional
The error returns after a power cycle — the control board likely needs professional replacement.
Gas supply lines, gas control valves, and venting should only be worked on by a licensed plumber or HVAC technician. Mains/line-voltage electrical work should be done with the breaker off and, beyond a simple reset, by a qualified electrician or plumber.
What the fix costs
A main control board replacement is one of the more expensive single-component repairs on this list — commonly $250–$600 installed (HomeGuide, Angi) — because the part itself costs more than a sensor or valve and a technician typically has to configure it after installing. Always confirm the power-cycle reset genuinely didn't clear the code before authorizing a board replacement, since that's worth ruling out first and costs nothing.
Related codes
- Navien E205 — H/E Outlet Error
- Navien E060 — Dual Venturi Limit Switch Error
- Water heater error code flashing or blinking
All Navien codes
Every Navien water heater fault code — the full list on one page.
Sources
- Navien NPE/NCB/NHB owner's manual and error code troubleshooting guide (manufacturer documentation)