Navien NPE-A / NPE-S Code E109
Fan motor fault. The fan motor is not running as expected. Navien gives one owner instruction and it is a good one: clean the intake air filter. A filter packed with lint makes the fan work against a restriction, and that is the cheap version of this fault.
Call a proThe verdict
Call a licensed plumber
Free to rule out. Clean the intake air filter first — it is Navien's only listed remedy and it is a ten-minute job. If the code stays, the fan is a real part with real labour on top.
Typical cost: $0–$900
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.
- Clean the intake air filter. This is the manual's entire owner-side remedy for this code.
- Listen when the unit tries to start — silence where the fan should spin up points at the motor rather than the filter.
- If a clean filter does not clear it, book a licensed professional.
Code E109 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: