Navien · Tankless Water Heater Serious

E003 — Ignition Failure

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.

Keep using it?
Limited use only
DIY difficulty
Moderate
Verified against
navieninc.com ↗

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.

Why it happens

Typical signs: No hot water · Unit clicks then shuts down · E003 flashes on front display · Burner does not light

  • 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).
  • Air in gas line Common after a new install or tank refill — line needs to be purged.
  • Dirty or misaligned flame rod Carbon buildup on the flame sensor prevents flame detection even when burner lights.
  • Faulty igniter or ignition wire Cracked ceramic igniter or broken HV lead — no spark at burner.
  • Gas valve failure Valve coil not opening or stuck closed.
  • Reversed polarity at outlet Hot/neutral swapped on the 120V supply will prevent flame rectification.

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.

More Navien tankless water heater codes

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) E046 E046 — Abnormality in Limit Control (Heat-Exchanger High-Limit)

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.