E003 Serious Moderate DIY

Navien Tankless Water Heater E003 — Ignition Failure

Navien Tankless Water Heater · Error code E003

What E003 Means

The unit attempted to ignite the burner but failed to detect a flame within the trial-for-ignition period. The gas valve closes for safety and the unit locks out.

Symptoms

  • No hot water
  • Unit clicks then shuts down
  • E003 flashes on front display
  • Burner does not light

Common Causes

1
Gas supply issue

Closed shutoff valve, empty propane tank, undersized gas line, or low inlet gas pressure (needs ~3.5" WC NG / 8" WC LP minimum under load).

2
Air in gas line

Common after a new install or tank refill — line needs to be purged.

3
Dirty or misaligned flame rod

Carbon buildup on the flame sensor prevents flame detection even when burner lights.

4
Faulty igniter or ignition wire

Cracked ceramic igniter or broken HV lead — no spark at burner.

5
Gas valve failure

Valve coil not opening or stuck closed.

6
Reversed polarity at outlet

Hot/neutral swapped on the 120V supply will prevent flame rectification.

How to Fix It

  1. Verify gas is ON at the shutoff and at the meter/tank; confirm tank is not empty (LP).
  2. Press the reset/power button — many post-install E003 events clear after the line purges air over 2-3 attempts.
  3. Check that other gas appliances run; if all are starved, the gas line is undersized or the regulator is bad.
  4. Measure inlet gas pressure under firing load — must meet manifold spec on the rating plate.
  5. Confirm correct outlet polarity with a plug-in tester; correct any reversed wiring.
  6. Pull and clean the flame rod with fine emery cloth; inspect igniter ceramic for cracks.
  7. If burner sparks but does not light, replace igniter; if it lights but locks out, replace flame rod.
  8. If pressures and components are correct, replace the gas valve assembly.

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 Navien flame rod View on Amazon→ Common replacement Navien igniter View on Amazon→

More Navien Tankless Water Heater Codes

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 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.