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
Other Navien series report code E109 under the same fault name, but each manual is transcribed separately and they do not read alike: