Navien E003: Ignition Failure

You press start on the shower and nothing happens — the remote controller shows E003 and the tankless unit never fires. This is the single most commonly reported Navien fault code, and in most cases it traces back to something upstream of the unit itself: gas, power, or grounding.

Applies to: Navien NPE, NCB, and NHB tankless and combi/condensing water heaters

What it means

Ignition Failure — the unit could not light the burner. This is the most commonly reported Navien fault code. It's a broad "tried and failed" code, so the cause can be as simple as a closed valve or as involved as a bad igniter — the checks below are roughly ordered from most to least likely.

Most common causes

Gas supply off or at inadequate pressure
Unit not receiving power, or a tripped breaker/GFCI
Ground wire not properly connected
Igniter not producing a spark
Flame rod issue

What you can safely check yourself

Confirm the gas valve is fully open at the unit and at the meter
Check that the unit has power and the breaker hasn't tripped
Power-cycle the unit

When to call a professional

The code returns after confirming gas and power, or you smell gas — grounding, igniter, and gas valve checks need a licensed technician.

Gas supply lines, gas control valves, and venting should only be worked on by a licensed plumber or HVAC technician. Mains/line-voltage electrical work should be done with the breaker off and, beyond a simple reset, by a qualified electrician or plumber.

What the fix costs

A service call for a no-ignition fault typically runs $150–$600 depending on region and what's found (Angi, Fixr water heater repair cost guides) — often the lower end if it's a closed valve or tripped breaker a technician resets, higher if an igniter or gas valve needs replacing. A replacement gas control valve commonly lands around $150–$450 installed. These are national ranges, not quotes; get a written estimate from a local licensed plumber or HVAC technician.

Related codes

All Navien codes

Every Navien water heater fault code — the full list on one page.

Safety. If you smell gas at any point, stop immediately, don't attempt to reset or relight the unit, ventilate the area, and call your gas utility or a licensed technician. Grounding and gas control valve work should be left to a qualified electrician or plumber, not worked around with repeated resets.

Sources

Navien NPE/NCB/NHB owner's manual and error code troubleshooting guide (manufacturer documentation)

This site is an independent reference, not a substitute for a licensed plumber or electrician. Gas water heaters can leak carbon monoxide, leak gas, or catch fire if serviced incorrectly. Anything involving the gas line, gas control valve, venting, or main electrical wiring should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.