Navien · Tankless Water Heater Moderate

E777 — Dip Switch Setting Error

The dip-switch configuration on the PCB is invalid or conflicts with the model — usually after a board replacement.

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

How to fix it

  1. Power off at the breaker.
  2. Open the front cover and locate the dip switches on the PCB.
  3. Compare every switch position to the table in the installation manual for your model and fuel.
  4. Set switches to the correct positions and power up.
  5. If E777 persists, verify the PCB part number is correct for this model.

Why it happens

Typical signs: E777 on display immediately after install or PCB swap · Unit will not start · No firing on demand

  • Incorrect dip switch positions Switches not set to match the model and fuel type (NG vs LP, altitude, cascade mode).
  • Wrong PCB for model Replacement board not configured for this unit.

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.