Navien E110: Air Pressure / Exhaust Blockage

On a Navien tankless water heater, error code E110 means the system detected abnormal air pressure or an exhaust blockage and shut down safely. This safety lockout stops active combustion, so there’s no immediate danger — but it won’t run again until the airflow issue is cleared.

Illustration of a vent termination blocked with debris, a common cause of exhaust or air-supply fault codes.

Likely Causes, Ranked

Dirty air intake filter
Dust and debris block the internal air intake filter enough to trip the pressure sensor.
Blocked vents
Ice, snow, leaves, or dirt blocking the outside intake or exhaust pipe terminations.
Clogged condensate drain
A slow or blocked condensate drain trap can prevent proper pressure equalization inside the unit.
Failed heat exchanger (rarer)
One source flags a malfunctioning heat exchanger as a possible cause over time — typically after ruling out the simpler causes above.

Step-by-Step Diagnosis

DIY SAFE
Check the outdoor vent terminations first

Clear snow, leaves, or debris from both the intake and exhaust pipe openings.
DIY SAFE
Clean or replace the internal air intake filter

Location varies by model; check your manual for the exact panel.
DIY WITH CAUTION
Check the condensate drain for clogs

A slow-draining or blocked condensate trap is a documented cause of E110.
DIY SAFE
If temps are below freezing

Some owners report E110 tied specifically to cold weather when temps stay below zero for several days (unconfirmed by the manufacturer) — worth checking for ice in the vent termination first.
PRO ONLY
If all of the above check out and the code persists

Have a technician check for a failing heat exchanger or a pressure-sensor fault.

Models Covered

NPE-A2 series, NPE-S2 series, NCB combi boiler series

FAQ

Can I fix Navien E110 myself?

Clearing a blocked vent, cleaning the intake filter, or clearing the condensate drain are all safe homeowner tasks. If those don’t fix it, call a technician.

What does Navien error code E003 mean and how can I fix it?

That’s a different code — ignition failure, not airflow. See our dedicated E003 page.

What does the E110 error code mean on a boiler?

Same family of issue on Navien’s combi boiler line: restricted combustion air or exhaust flow.

How do I reset a Navien error code?

Fix the cause first, then power-cycle. E110 in particular won’t clear on its own if the vent or filter is still blocked.

Written by HotWater Decoded — water heater repair specialists. Technically reviewed by a licensed technician on our team.

Sources

Google’s AI Overview summary, citing JustAnswer
A Reddit r/Plumbing thread on a temperature-related E110 pattern