Navien · Tankless Water Heater Moderate

E615 — Abnormal Input/Memory (MCU Internal Fault)

Per the Navien NPE-series manual, E615 means an abnormal input/memory fault internal to the unit's main microcontroller (MCU) — not a wall-controller communication error, despite what may be a widely repeated assumption for E6xx-family codes.

Keep using it?
Yes, with caution
DIY difficulty
Hard
Verified against
navieninc.com ↗

How to fix it

  1. Power off the unit at the breaker for several minutes to force a full reset.
  2. Restore power and check if E615 clears.
  3. If E615 returns, this is an internal main control board fault — have a qualified technician diagnose and replace the main PCB if needed rather than replacing the wall controller.

Why it happens

Typical signs: E615 on display · Unit behaves erratically or will not hold settings · Possible lockout requiring a power reset

  • Internal MCU fault The main control board's microcontroller has detected an invalid internal memory read/write — this is an internal main-board fault, not a fault in the remote wall controller.
  • Power surge or brownout A voltage event can corrupt the MCU's memory state.

Parts you may need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

  • Navien main control board (PCB) Common replacement
    Amazon →

More Navien tankless water heater codes

E003 E003 — Ignition Failure E003C E003C — Cascade Ignition Failure E012 E012 — False Flame / Flame Loss E016 E016 — Overheat / High-Limit Trip E027 Tankless E027 — Sensor Abnormality E030 E030 — Abnormal Exhaust Temperature (Flue Overheat)

All Navien codes → All tankless water heater codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: navieninc.com.