Navien Error Code E110: What It Means and What to Check
Quick answer: Navien E110 is the error code that means “abnormal air pressure.” The heater has detected that air is not moving through the exhaust and intake path the way it expects, so it shuts down. Navien’s user manual gives two owner-level checks: make sure the exhaust pipe is free of obstructions, and clean the intake air filter. Press Reset once after those checks. If E110 returns, the cause is usually in the vent run, the condensate drain, or the fan, and that needs a technician.
No code on the display, and the water is just lukewarm? See tankless water heater not heating.
Safety first: E110 is an exhaust-path code on a gas appliance. If you smell gas, Navien’s instructions are to not light any appliance, not touch any electrical switch or phone in the building, and call your gas supplier from a neighbor’s phone, or the fire department if you cannot reach the supplier. If anyone in the home feels dizzy, nauseous, or has a headache, leave and call emergency services; those are carbon monoxide symptoms. Never run the heater with any part of the intake or exhaust disconnected, and do not remove the front cover while the heater is powered.
In this guide
What Navien E110 means
Navien’s NPE user’s information manual lists E110 as Abnormal air pressure. The heater uses a sensor to confirm that the fan is moving combustion air in and exhaust out at the expected rate. When the reading is outside its range, the control stops the burner and shows E110. The same manual notes that a clogged intake air filter will stop the unit and show error code 110, which is why the filter is the first thing to check.
E110 is about airflow, not water temperature or gas supply. Related codes you may see on the same unit: E012 (flame loss) and E003 (ignition failure) point to the burner rather than the air path, and E109 (fan motor) shares the intake-filter check.
Owner-level checks from the Navien manual
- Check the vent terminals outside. Navien says not to place anything in or around the vent terminals and to inspect the vent termination and air intake annually. Look for leaves, snow, ice, a bird’s nest, insulation, or anything stacked against the terminal. Clear it only from the outside; do not open the vent pipe.
- Clean the intake air filter. Navien’s manual lists this as an owner task to do every three to four months. The published procedure is: press Power to turn the heater off, disconnect the power supply, remove the front cover, remove the screw holding the air intake filter at the top left, pull the filter out, clean it with a toothbrush under running water, let it dry completely, refit it, secure the screw, replace the cover, reconnect power, and press Power. Follow the version in your own manual, since the filter location differs between models.
- Press Reset once. Navien’s manual says you can try resetting the water heater to clear an error message. Some controllers use a Reset button; others use Back. If the code clears and stays clear, note the date in case it comes back.
- If E110 returns, stop. Navien’s instruction is that if the listed remedies do not resolve the problem, contact Technical Support (1-800-519-8794 in the U.S.) or your installer. Repeated resets do not fix an airflow fault.
What a technician looks at for E110
| Area | Why it causes E110 | Why it is not an owner job |
|---|---|---|
| Vent length, elbows, and material | A run that is too long, has too many turns, or uses the wrong pipe restricts airflow | Needs the installation manual’s vent tables and the original installation details |
| Vent joints and seals | A separated or leaking joint lets exhaust recirculate into the intake | Exhaust can contain carbon monoxide; joints are checked with the heater running |
| Condensate trap and drain | Condensate that cannot drain collects in the exhaust collector and changes the pressure the sensor reads | Involves disconnecting the trap from the heat exchanger outlet; see below |
| Fan and air pressure sensor | A fan that cannot reach speed, or a sensor with a blocked or kinked hose, reads as abnormal pressure | Internal components behind the cover; tested with the unit energized |
| Wind at the terminal | Strong wind into an exhaust terminal can push the reading out of range | Fix is a different terminal or location, which is installation work |
E110 and the condensate trap
A condensing tankless heater produces water as it runs. That water leaves through a condensate trap and drain line. If the trap or line is blocked, the water has nowhere to go and backs up toward the exhaust side of the heat exchanger, which can trigger an air-pressure code. Signs that point this way: water on the floor under the heater, a trap that is overflowing or dry when it should hold water, or a drain line that has sagged or frozen.
Our separate guide to a leaking Navien condensate trap covers the trap, hose, and drain-line checks in detail. Navien’s user manual does not list the condensate system as an E110 remedy, so treat a suspected condensate problem as something to describe to the technician rather than something to clear by disconnecting the trap yourself.
Check whether your unit is in the 2019 recall
In 2019 the U.S. Consumer Product Safety Commission announced a recall of Navien NPE-180A, NPE-180S, and NCB-180E units manufactured between July 9 and October 14, 2018, because a propane conversion kit could cause them to produce excessive carbon monoxide. If you have one of those models running on propane, the CPSC notice says to stop using it and contact Navien for a free replacement kit, and to have a working carbon monoxide alarm outside sleeping areas in the meantime. The manufacture date is encoded in the serial number. Details are on the CPSC recall page. This recall is separate from E110, but an exhaust-related code is a reasonable prompt to check it.
What to tell the technician
- Full model number (for example NPE-240A2) and the serial number from the rating plate.
- Whether E110 appears at startup, during long hot-water use, or only in certain weather.
- What you found at the vent terminals and the intake filter, and whether a reset cleared it and for how long.
- Any water under the heater or around the condensate trap.
- Whether the venting was changed, extended, or had work done nearby recently.
Frequently asked questions
Can I keep using the water heater with E110?
The heater will not run while the code is active, and that is by design. Do not try to bypass it. Clear the code only with the owner checks above and a single reset; if it returns, arrange service.
Is E110 dangerous?
The code itself is the heater protecting you by refusing to run with abnormal airflow. The risk is in ignoring the cause. Any exhaust-path problem on a gas appliance deserves a working carbon monoxide alarm and a prompt service visit.
Does E110 mean the fan has failed?
Not necessarily. A fan fault is one possibility, but Navien’s own first checks are the exhaust pipe and the intake filter. Fan and sensor testing is a technician task.
How often should I clean the intake air filter?
Navien’s manual says every three to four months. A heater in a dusty utility room or garage may need it more often.
Why does E110 come back in winter?
Cold weather brings ice and snow at the terminals, more condensate, and a higher chance of a frozen drain line. All three can restrict the air or water path. Mention the seasonal pattern to the technician.
References: Navien NPE2 series user’s information manual (error code table, intake air filter cleaning, reset, safety information) · Navien NPE operation manual · CPSC recall notice, 2019. Your model’s own manual takes priority.
Published October 16, 2026. Written and edited by Jordan Hale. General educational guidance; follow your exact model instructions and use a qualified technician for anything behind the front cover or in the vent system.
