E016 Critical Moderate DIY

Navien Tankless Water Heater E016 — Overheat / High-Limit Trip

Navien Tankless Water Heater · Error code E016

What E016 Means

The high-limit switch or overheat sensor detected unsafe heat-exchanger temperature. The burner is locked out until reset.

Symptoms

  • Hot water then sudden shutdown
  • E016 on display
  • Heat exchanger hot to the touch
  • Repeated lockouts on long draws

Common Causes

1
Scale buildup in heat exchanger

Calcium scale insulates the exchanger and drives wall temps up — most common cause in hard-water areas.

2
Restricted water flow

Clogged inlet screen, partially closed isolation valve, or fouled aerators reduce flow below safe threshold.

3
Failed flow sensor / turbine

Under-reporting flow lets the burner over-fire for the actual GPM.

4
Blocked flue or intake

Reduced combustion airflow causes incomplete heat transfer and exchanger overheating.

5
Failed high-limit switch

Open or drifting switch trips prematurely.

6
Failed outlet thermistor

Mis-reading temp causes runaway firing.

How to Fix It

  1. Reset the unit; if it trips again under heavy draw, suspect scale or flow.
  2. Descale the heat exchanger with white vinegar or a tankless cleaner via the service ports (3-4 hour circulation).
  3. Clean the cold-side inlet filter screen (it traps debris that chokes flow).
  4. Inspect the venting for blockage, nests, or sagging that traps condensate.
  5. Test the high-limit fuse/switch for continuity; replace if open at room temp.
  6. Check outlet thermistor resistance against spec; replace if drifted.
  7. If symptoms persist after descale and parts check, replace the flow sensor.

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.

Common replacement Tankless descaler kit View on Amazon→ Common replacement Navien high-limit switch View on Amazon→ Common replacement Navien flow sensor View on Amazon→

More Navien Tankless Water Heater Codes

E003 E003 — Ignition Failure E003C E003C — Cascade Ignition Failure E012 E012 — False Flame / Flame Loss E027 E027 — Gas Type Setting Error E030 E030 — Fan / Combustion Blower Fault E046 E046 — Mixing Valve Error

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.