Navien NPE-A / NPE-S Code E004
False flame detection. The unit is detecting a flame when there should not be one. Navien's only owner-facing instruction is to make sure the electrical cord is properly grounded — a grounding fault makes the flame rectification circuit report a flame that is not there.
Call a proThe verdict
Call a licensed plumber
A flame safety circuit reporting something impossible. Grounding is Navien's one check and it is worth confirming the unit is on a properly grounded outlet; everything else is the flame rod and the board.
Typical cost: $150–$800
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the NPE-A / NPE-S — not averaged across the brand.
Source: Navien NPE Operation Manual (NPE-A / NPE-S) (p. 16), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- Confirm the heater is plugged into a properly grounded outlet and that nothing has been changed in the wiring recently.
- Do not keep resetting it to force a run — this is a flame safety device reporting a fault.
- Book a licensed professional.
Code E004 on other Navien series
Other Navien series report code E004 under the same fault name, but each manual is transcribed separately and they do not read alike:
Don't confuse this with
One other Navien NPE-A / NPE-S code points at flame detection too. They are the same symptom reported from a different place in the unit, so which one the display shows is what tells you where to look: