Navien NPE-A / NPE-S Code E110
Abnormal air pressure. The unit is not seeing the air pressure it expects across the combustion path. Navien names two owner checks: that the exhaust pipe is free of obstructions, and that the intake air filter is clean. Both are about the same thing — the unit's ability to move air through itself.
Call a proThe verdict
Call a licensed plumber
Often free. A blocked vent terminal or a dirty intake filter is the common cause and both are visible without opening the heater. What you must not do is run it with any vent section disturbed.
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.
- Go outside and check the exhaust and intake terminals: snow, leaves, a nest, or something built too close will all do this.
- Clean the intake air filter.
- Do not disconnect or reseat vent pipe yourself — a badly sealed joint leaks exhaust gas into the building.
- If both are clear and the code stays, book a licensed professional.
Code E110 on other Navien series
Other Navien series report code E110 under the same fault name, but each manual is transcribed separately and they do not read alike: