Navien E004: False Flame Detection

The unit shuts itself down mid-cycle and E004 appears on the display, even though nothing looks obviously broken. That's because this code isn't reporting a missing flame — it's reporting a flame signal the control board doesn't trust, which points the troubleshooting in a different direction than most fault codes.

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

What it means

False Flame Detection — the control board is registering a flame signal when no flame should be present. Because the unit is designed to shut down rather than keep running on a signal it can't verify, this code is the water heater protecting itself, not malfunctioning on its own.

Most common causes

Loose or improperly connected ground wire
Flame rod fault
Internal gas valve leak

What you can safely check yourself

Check that the unit's power cord is plugged into a properly grounded outlet and the ground wire connection is secure

When to call a professional

The grounding check doesn't clear the code, or the code repeats — this needs a technician to inspect the flame rod and gas valve.

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

Because this code often traces back to a grounding issue you can check yourself, many E004 calls end up being a simple $75–$250 service visit (Angi, HomeGuide) once a loose ground wire is reseated. If the flame rod or an internal gas valve leak turns out to be the actual cause, expect the higher end of the usual $150–$600 diagnostic range, with a gas valve replacement running roughly $150–$450 installed.

Related codes

All Navien codes

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

Safety. A flame-detection fault that traces back to an internal gas valve leak is not something to keep resetting past. If the code returns right after a power cycle, or you notice any gas odor near the unit, stop and call a licensed technician rather than continuing to restart it.

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.