E777 Moderate Moderate DIY

Navien Tankless Water Heater E777 — Dip Switch Setting Error

Navien Tankless Water Heater · Error code E777

What E777 Means

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

Symptoms

  • E777 on display immediately after install or PCB swap
  • Unit will not start
  • No firing on demand

Common Causes

1
Incorrect dip switch positions

Switches not set to match the model and fuel type (NG vs LP, altitude, cascade mode).

2
Wrong PCB for model

Replacement board not configured for this unit.

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.

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 E027 — Gas Type Setting Error E030 E030 — Fan / Combustion Blower Fault

All Navien codes → All tankless water heater codes →

Verified against manufacturer documentation: navieninc.com

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.