Tankless water heater error help

Navien E110 Error Code? Check the Intake and Exhaust

Navien E110 is an abnormal-air-pressure shutdown. Start outside: turn the heater off, check the intake and exhaust terminations for debris, ice, or a packed screen, then look for condensate backup or visible vent damage before buying parts.

A blocked termination, clogged intake screen, backed-up condensate path, or sagging vent pipe fits the code better than a failed board.

Use the code as a sorting tool: outside blockage first, drainage second, visible vent condition third, internal airflow diagnosis last.

Don’t start with: Do not keep resetting, alter vent pipe, open sealed combustion parts, or touch gas components. Gas smell or exhaust smell means stop and call a pro.

First safe checkWith the heater off, look at both outside vent openings for leaves, lint, snow, ice, nests, or a packed screen.

Stop pointGas smell, melted venting, loose exhaust joints, carbon-monoxide alarm, or repeat E110 after one restart means stop and call a pro.

Do this before another reset

Turn the heater off before touching the vent termination or looking near condensate tubing.
If you smell gas, leave the area and call the gas utility or call a pro. Do not keep testing the heater.
If a carbon-monoxide alarm sounds, leave the building and call emergency services. Do not troubleshoot indoors.
Stop if the exhaust pipe is loose, cracked, melted, scorched, disconnected, or sloped so water can sit in it.
Do not open sealed combustion parts, fuel piping, burners, pressure tubes, or the cabinet interior unless you are qualified to service tankless equipment.

Prepared by: Repair Riot Last updated: 2026-06-15 How we build and check guides

What E110 pattern do you have?

Code started after snow, wind, rain, or yard work?

Check the outdoor intake and exhaust ends first. Debris, snow, ice, lint, or a blocked screen can trigger E110 quickly.

Code returns immediately after one restart?

Stop resetting. A repeat code with clear vent ends points to condensate, vent slope, pressure sensing, blower, or combustion-side diagnosis.

Hot water runs briefly, then E110 appears?

Look for a partial vent restriction, condensate drainage problem, or sagging visible vent run before suspecting a control part.

You see water near vent or condensate tubing?

Check for a kinked tube, full neutralizer, blocked outlet, or vent low spot. Stop if water reaches wiring or the cabinet interior.

Do you smell fuel odor or exhaust?

Shut the heater down, leave the area if fuel odor is present, and call a pro. Do not restart for another test.

What to check before service

Use these views as safe inspection patterns: the closed heater and vent path, the outdoor terminations, and the condensate drain area. Do not open sealed combustion parts.

Closed condensing tankless water heater with two separate PVC pipes rising from the top collars to side-by-side wall penetrations — This representative indoor view keeps the two vent paths separate from the heater collars to the wall. Use the exact model manual to identify intake and exhaust before inspecting outside.

White PVC two-pipe snorkel termination with a screened intake facing down and a taller screened exhaust riser terminating outward — A common two-pipe snorkel arrangement turns the intake down and raises the exhaust above it before terminating outward. Keep both openings clear and confirm the exact clearances and approved parts in your model manual.

Single condensate tube descending from a closed condensing tankless heater to a floor drain with an air gap — This representative view makes the visible checks clear: one continuous route, no kink or sag, and a safe drain termination. Follow the exact model manual for the real installation.

Before you buy any part

Match the exact Navien model and the confirmed diagnosis. E110 does not mean a blower, board, or sensor should go in the cart. Buy maintenance items only after a visible test points there: blocked vent end, kinked condensate tube, spent neutralizer media, or a confirmed service finding.

Jump to: Tools You May Need · When to call a tech

What E110 is really warning about

Navien E110 is about air pressure and combustion airflow, not a random electronics failure. A good clue is timing: weather, yard debris, or recent vent work points outside before parts.

A blocked intake or exhaust termination can starve the burner for air or keep exhaust from leaving correctly.
Snow, ice, lint, leaves, insect nests, and packed screens are common visible triggers after weather or yard work.
Condensate backup can upset airflow or pressure readings if water collects where it should drain away.
A sagging or separated vent run is a stop point because exhaust movement and carbon-monoxide safety are involved.

What not to do first

Usually, the safe move is to treat E110 as an airflow shutdown, not a combustion-appliance repair experiment. Gas smell during any check means stop and call a pro.

Do not keep resetting E110 to get through another shower. One controlled restart after safe checks is enough.
Do not open sealed combustion parts, pressure tubes, burners, fuel valves, or internal wiring.
Do not tape, glue, drill, shorten, or reroute vent pipe as a quick fix. Venting must follow the approved installation method.
If you smell gas, smell exhaust, see scorching or melted plastic, or hear a carbon-monoxide alarm, leave the area and call a pro.

Work through the safe visible checks

Stay with checks you can do with the heater off and the cabinet closed. Watch for debris, water marks, and shifted vent supports before the clue moves into service work.

Turn the heater off at the control or accessible plug. Do not remove the front cover for this first pass.
Look at both outdoor vent openings from the ground. Clear loose leaves, lint, snow, ice, or nest material only from the opening you can reach safely.
Check the visible vent run indoors for sagging, separation, scorch marks, water staining, loose couplings, or sections that shifted after storage or nearby work.
Look at the condensate tubing and neutralizer if installed. A kinked tube, blocked outlet, or full neutralizer can move condensate up the suspect list.
After the visible checks are clean, do one controlled restart and run one hot-water fixture. If E110 returns, stop there.

How to read the result

The result should tell you whether this was a simple outside restriction or a service call. Do not use repeated resets as a test method.

What you find	What it means	Next move
Debris, snow, ice, lint, or nest at vent end	Likely intake or exhaust restriction	Clear only reachable loose material, restart once, and watch for repeat E110.
Kinked condensate tube or blocked neutralizer outlet	Condensate may be backing up into the wrong path	Correct only simple visible kinks or blocked outlets; call service if water is inside the heater.
Vent sag, loose joint, scorching, or melted pipe	Unsafe venting or exhaust issue	Leave heater off and call a qualified tankless service tech.
Vent ends look clear but E110 returns	Internal pressure, blower, sensor, or hidden vent issue	Stop buying parts and schedule diagnosis.
Fuel odor or carbon-monoxide alarm	Immediate life-safety issue	Leave the area and call emergency services, the utility, or a qualified pro.

Tools You May Need

These tools are for visual inspection and gentle exterior clearing. They do not make combustion, vent, or fuel-system repairs DIY-safe; call a pro for those.

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Inspection flashlight

Helps when: You need to see the vent termination, visible vent run, condensate tube, or neutralizer without opening the heater.

Skip it when: You smell gas, the carbon-monoxide alarm sounds, or the check requires opening sealed combustion parts.

Compare inspection flashlights on Amazon

Soft nylon brush

Helps when: Loose lint, leaves, or light debris is sitting at the outdoor intake or exhaust opening and can be cleared from the end.

Skip it when: Debris is deep inside the pipe, the vent is high, icy, damaged, or you would need a ladder or roof access.

Compare soft nylon brushes on Amazon

When to call a tech

Call sooner when the clue touches gas, exhaust, carbon monoxide, hidden venting, or internal pressure sensing.

Call a qualified tankless service tech if E110 returns after one safe restart with clear vent openings.
Call a licensed pro for loose, melted, cracked, disconnected, or incorrectly sloped venting.
Call immediately if you smell fuel odor or exhaust near the unit. Leave the area if gas odor is present and call a pro.
Do not troubleshoot indoors if a carbon-monoxide alarm sounds; leave the building and call emergency services.
Use the exact model and serial number before any internal part is ordered.

What a good result looks like

A real fix clears the code without repeated resets and leaves the vent, condensate, and combustion paths safe.

The heater runs one nearby hot-water fixture for several minutes without E110 returning.
Both outdoor vent openings stay clear while the heater operates.
No water drips, gurgles, or backs up around the condensate tube or neutralizer.
There is no gas smell, exhaust smell, scorching, loose vent joint, or carbon-monoxide alarm.

FAQ

Can I keep resetting a Navien E110 code?

No. Do one restart only after checking the outdoor vent openings and obvious condensate clues. If E110 returns, leave the heater off and schedule service.

Does E110 mean the blower motor is bad?

Not by itself. Blocked vent terminations, condensate trouble, or visible vent issues come first. A blower or pressure-sensing fault needs diagnosis before parts are ordered.

Can cold weather cause E110?

Yes. Snow, ice, wind-driven debris, and frozen condensate can block airflow or drainage. Check the vent ends from the ground before opening the heater.

Is it safe to use the heater with E110 showing sometimes?

No. The code is tied to combustion airflow or exhaust movement. Treat it as a safety shutdown until the cause is found and corrected.

What if I smell gas near the water heater?

Do not keep testing. Leave the area, avoid switches or flames, and call the gas utility or call a pro.

What if my carbon-monoxide alarm goes off?

Leave the building and call emergency services. Do not troubleshoot the heater indoors while a carbon-monoxide alarm is active.

Can I clean the vent myself?

You can clear loose debris at a safe ground-level termination with the heater off. Do not reach deep into the pipe, climb onto a roof, or alter the venting.

What should I tell the service tech?

Tell them when E110 started, whether it followed weather or vent work, what you found at the vent ends, whether condensate looked backed up, and whether one restart changed anything.

Sources and safety context

This page uses Navien manual context, combustion-airflow safety rules, and public carbon-monoxide safety guidance. Sources are used for diagnosis boundaries, not copied wording.

Navien NPE-2 user manual — Lists E110 as abnormal air pressure and points users toward exhaust/intake checks.
EPA carbon monoxide safety for fuel-burning appliances — Supports professional inspection of gas water heaters, flues, and vents and the fresh-air and emergency-help stop points.
Navien NPE-2 installation and operation manual — Shows the approved termination types and the standard two-pipe sidewall example used to check the vent images.