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
The same code number can mean something different on another series — make sure you're reading the page for your exact unit:
Don't confuse this with
One other Navien NPE-A / NPE-S code points at flame detection too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: