Navien Water Heater Error E110 – Causes & Fix
The fan can't move enough air through the vent system – most often a clogged intake filter or a buried vent.
Safety first · Consult a professional
Because E110 involves the flue path, treat any CO alarm as genuine: get everyone outside into fresh air, call 911, and leave the heater off until a professional has checked the venting. If you smell gas, don't flip switches or use a phone indoors – leave the house and call 911 or your gas utility from outside.
- Gas appliance: no DIY repairs. If you smell gas, leave the building, do not use switches and call your gas utility’s emergency line from outside.
- Carbon monoxide is odorless. Keep a CO alarm near fuel-burning appliances; if it sounds, get everyone outside and call 911.
At a glance
Severity: High
- Meaning
- Abnormal Air Pressure – Intake or Exhaust Blocked
- Typical repair cost
- $0–$900
- DIY difficulty
- Moderate
E110 tells you the Navien's combustion air path is restricted. The NPE-A2/S2 tankless manuals call it "abnormal air pressure" and the NCB-H combi manual calls it "exhaust blockage"; both describe the same thing. An air pressure sensor compares what the fan should be producing with what it actually sees, and when the intake or exhaust is choked the control shuts the gas valve so the burner can't run on starved, incomplete combustion. Navien lists exactly two owner remedies – clean the intake air filter and make sure the exhaust pipe is free of obstructions – and the manual states outright that a lint-clogged filter will stop the heater with this code. If the filter is clean and both terminals are clear, the cause is in the venting, the condensate path, the sensor or the fan, and that belongs to a licensed plumber or HVAC technician.
How it looks on the display
Model families & display variants
| Model family | Shows | Note |
|---|---|---|
| NPE-A2 / NPE-S2 condensing tankless | E110 | User manual wording: abnormal air pressure. Front-panel display; reset with the Back button. |
| NCB-E / NCB-H condensing combi boilers | E110 | NCB-E lists abnormal air pressure, NCB-H lists exhaust blockage. The owner checks are identical: exhaust pipe clear, intake filter clean. |
| NaviLink Wi-Fi app | E110 | The app only relays the fault; do the filter and terminal checks at the unit and clear the code there. |
Symptoms
- No hot water and E110 on the front panel, sometimes returning a few minutes after a reset
- Code appears after heavy snow, an ice storm or strong wind at a side-wall vent
- Fan sounds louder than usual or surges just before the shutdown
- Heater copes with one tap but locks out when several fixtures run at once
- Unit lives in a laundry room, garage or dusty utility space
Possible causes
Ranked by how often each cause is behind this code (editorial estimate).
- Intake air filter clogged with lint or dust – Navien's manual names this directly as a trigger for E110
- Intake or exhaust terminal outside blocked by snow drift, ice, a bird or wasp nest, leaves or a clogged screen
- Condensate not draining (kinked, frozen or blocked line) so water backs up into the exhaust side
- Vent installation problem: run too long, too many elbows, a sagging section holding water or a joint pulled apart
- Air pressure sensor or its sensing tube faulty, cracked or disconnected
- Fan motor weak or dirty (often logged together with E109)
Fix it step by step
Rule out gas odor and CO first
If a CO alarm is sounding or there's any gas smell, stop here and follow the safety box. Only continue with the checks below when the air in the room is normal.
Clean the intake air filter
Turn the heater off with the Power button and unplug it. On NPE-A2/S2 units the filter sits behind the front cover at the top left, held by one screw; slide it out, scrub it with a soft brush under running water and let it dry completely before refitting. Navien recommends doing this every 3–4 months, more often in a laundry area.
Tools: Screwdriver, Soft brush
Walk outside to both terminals
Find the intake and exhaust pipes where they leave the house and look for snow, ice, nests, leaves or a blocked screen. Clear what you can reach by hand, keep at least 12 inches of open space around them, and never push tools into the pipe or pull vent sections apart.
Tools: Flashlight, Gloves
Check the condensate drain
Follow the small drain line from the bottom of the heater to the floor drain or condensate pump. It must slope downward, must not be kinked, frozen or submerged, and a condensate pump (if fitted) should switch on when its reservoir fills.
Tools: Flashlight, Towels & shallow pan
Reset once and watch
Press the reset (Back) button, open a hot tap fully and listen: pre-purge fan, ignition, steady burner. Note whether E110 returns immediately or only after a few minutes at high flow – that timing helps the technician.
Hand over the details
If the code comes back, write down the model (for example NPE-240A2), the vent material and rough length, and when the fault occurs. A licensed plumber or HVAC tech can then check the vent run, the pressure sensor and the fan, or you can call Navien technical support at 1-800-519-8794.
How to reset E110
- Confirm there's no gas smell, the intake filter is clean and both vent terminals are clear.
- Press the reset button on the front panel (the Back button on NPE-A2/S2 models).
- Open a hot tap fully and watch for a couple of minutes while the unit purges, lights and settles.
- If E110 reappears, leave the unit off and book a service visit instead of resetting again and again.
Where the parts are
- 1Flue
- 2Fan
- 3Heat exchanger
- 4Ignition electrode
- 5Gas valve
- 6Circulation pump
- 7Expansion tank
- 8Pressure gauge
- 9Temperature sensor
Repair options & costs
| Repair | DIY? | Estimated cost |
|---|---|---|
| Clean the intake air filter (owner maintenance) | Yes | $0–$10 |
| Clear blocked condensate line or trap (service visit) | No | $120–$250 |
| Replace air pressure sensor or sensing tube | No | $180–$380 |
| Raise, relocate or rework vent termination / vent run | No | $300–$900 |
| Replace fan (blower) assembly | No | $350–$750 |
Rough US estimates; technician call-out fees vary by region. Not a quote.
When to call a technician
Call a licensed plumber or HVAC technician if E110 returns after the filter is cleaned and both terminals are clear, if it happens after every heavy snowfall (the termination may need raising), or if a CO alarm has ever sounded near the heater. Opening the vent system, testing the pressure sensor and replacing the fan are professional jobs.
Frequently asked questions
Why does my Navien show E110 every time it snows?
Side-wall terminals mounted close to the ground get buried by drifting snow, which chokes the intake or exhaust. Clearing them gets you going again, but a permanent fix is having the installer raise the termination above the expected snow line.
How often should I clean the Navien intake air filter?
Navien suggests every 3–4 months. In laundry rooms or garages with lint and sawdust, checking it monthly is sensible, because a clogged filter is one of the documented triggers for E110.
What's the difference between E109 and E110?
E109 points at the fan motor itself, while E110 is the air pressure reading being out of range. They often appear together because a restricted vent makes the fan struggle, so both send you to the filter and vent first.
Can I run the heater without the intake filter until I buy a new one?
No. The filter keeps lint and dust out of the fan and burner; running without it lets debris build up inside where only a technician can clean it. Wash and dry the original filter instead – it's reusable.
Sources
- Official Navien user documentation and support pages (facts only; wording is our own)
- Methodology: How We Build Code Pages · Data Sources We Use · Editorial Policy