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
The same code number can mean something different on another series — make sure you're reading the page for your exact unit: