E004
Navien Tankless Water Heater
Severity: CriticalWhat it means
Navien E004 is a false-flame error: the flame-sensing rod is reporting a flame when the gas valve is closed and there shouldn't be one.
Because the unit can't trust that reading, it shuts down on safety.
The usual cause is a flame rod that's contaminated, shorted to the burner, or wet with condensate — or a stuck gas valve actually leaking a little gas.
It is treated as a safety fault, so don't ignore it.
Affected Models
- Navien NPE-180A, NPE-210A, NPE-240A (Classic)
- Navien NPE-180S, NPE-210S, NPE-240S
- Navien NPE-2 series (NPE-180A2, NPE-210A2, NPE-240A2)
- Navien NCB-E combi-boilers
- Navien NPN series condensing tankless units
Common Causes
- Flame-sensing rod coated with soot, scale, or oxidation
- Flame rod cracked or its insulator shorting to ground
- Condensate pooling around the burner from a clogged condensate trap or drain line
- Damp combustion air being pulled in from a poor intake location
- Wiring to the flame rod chafed or grounded
- Gas valve not closing fully (leaking by) — the serious case
How to Fix It
-
Power-cycle once and see if it clears.
Turn the unit off at the panel, wait ten seconds, turn it back on.
A one-off E004 from a brief condensate splash sometimes won't return.
If it comes back the same day, there's a real cause to chase. -
Clear the condensate drain.
Condensing tankless units make acidic water that drains out the bottom.
If the trap or drain hose is plugged, that water backs up toward the burner and fools the flame rod.
Disconnect the condensate hose, flush the trap, and make sure the drain runs freely downhill with no kinks. -
Clean or replace the flame rod.
Breaker off.
The flame-sensing rod is a thin metal probe near the burner.
Gently clean the tip with fine abrasive pad or fine sandpaper, check the white ceramic insulator for cracks, and reseat the wire.
If the insulator is cracked, replace the rod — they're cheap. -
Check where combustion air comes from.
If the intake pipe pulls air from a damp crawlspace, near a dryer vent, or somewhere that gets wet, moisture rides in with it.
Rerouting the intake to dry outdoor air can stop recurring E004. -
If it persists, get the gas valve checked.
A flame signal with the valve commanded shut can mean the valve is passing a trace of gas.
That's a safety issue — shut the gas off to the unit and have a qualified tech inspect or replace the gas valve.
Don't keep resetting past this point.