Navien E110 Error Code: Exhaust and Venting Blockage

Quick Answer

Navien E110 is a venting fault. The sub-code tells you where: E110-01 means the outdoor vent termination cap is physically blocked by a bird nest, ice dam, or debris. E110-02 means the issue is inside, usually a kinked vent pipe, pipe that is too long, or a condensate drain that is backed up and pressurizing the flue.

E110 is the code that has me driving out in January more than just about anything else. Navien shuts the burner down on purpose here, because a blocked exhaust means CO has nowhere to go. The good news is, it's almost always a quick fix: ice, a bird nest, or a backed-up condensate trap. But keep resetting it without fixing the actual blockage and you'll eventually trash the pressure switch too.

NavienWaterheaterSeverity: high82% DIY Success

Time to Fix

20–60 min

Difficulty

beginner

Parts Cost

$15 – $80

Tools Needed

Flashlight, Work gloves and safety glasses

What Does the E110 Code Mean?

OK so E110 is basically Navien saying 'something's choking off the exhaust and I'm not running like this.' The pressure switch detects that air isn't moving through the vent system the way it should and locks the unit out. Most of the time you'll see it in winter when condensate freezes solid at the outdoor cap. But spring's almost as bad because that's nesting season and birds love those termination caps.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Bird nest or animal debris in vent termination cap40%

Ice dam forming around exhaust outlet in freezing temperatures24%

Kinked or crushed flexible vent pipe14%

Condensate drain line blocked, backing up into flue12%

Vent run exceeds maximum allowable length10%

Symptoms You May Notice

E110-01 or E110-02 flashing on the display and the unit won't stay lit, it tries to fire, runs for maybe a second, then cuts out and shows the code again.
You can hear it trying: there's the click of the igniter and a brief whoosh of flame, then silence, then lockout.
In winter, a thick ring of ice hanging off the exterior vent cap, or the cap opening is completely frosted over.
The condensate drain line has water backing up out of it instead of draining away normally.
Hot water runs for 30 seconds then goes cold because the unit locked out mid-cycle and you didn't notice until the shower hit you.

Can you reset a Navien waterheater to clear the E110 code?

Clear the blockage first. Resetting without fixing anything just brings the code right back in 30 seconds. Once the vent is clear, press the Info button on the Navien controller three times. The unit will attempt ignition. If it clears, run a hot water tap for 2 full minutes to confirm it's stable. If it doesn't clear, cut power at the breaker for 30 seconds, restore, and try again. Still coming back? The blockage isn't fully cleared, or the pressure switch is bad.

Tools Required for Diagnosis

FlashlightWork gloves and safety glassesPhillips #2 screwdriverFlathead screwdriverBucket and clean water (for condensate trap flush)Kettle of warm water or heat gun on low setting (for ice removal only, never open flame)Foam pipe insulation (optional, for freeze prevention)

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name	OEM Number	Estimated Price
Vent Termination Cap (2-inch, PVC)BH-2T (various, check vent brand) · $15–$40	BH-2T (various, check vent brand)	$15 – $40
Condensate Trap Kit30010723A · $20–$35	30010723A	$20 – $35
Air Pressure Switch30010617A · $45–$80	30010617A	$45 – $80

Frequently Asked Questions

Why does my Navien show E110 only in winter?

Navien condensing heaters pull so much heat out of the combustion gases that those gases cool enough to form liquid condensate before they exit the flue. That liquid drips out at the exhaust termination cap, and when it's below freezing outside, it refreezes right at the opening. Enough buildup and it chokes off the vent enough to trip the pressure switch. The immediate fix is clearing the ice. The real fix is making sure your vent pipe has a slight slope back toward the unit's condensate trap so liquid drains inward instead of pooling at the cap.

What is the difference between E110-01 and E110-02?

Think of it this way: E110-01 is Navien saying the problem is outside, the termination cap is blocked. E110-02 is Navien saying the pressure readings inside are off, which usually means the vent pipe run itself is the problem, too many bends, too long, a crushed section, or the condensate trap is backed up and creating back-pressure in the flue. You can also get E110-02 from a failing air pressure switch inside the unit, especially on older installs past 8 years. Start with the external stuff first since it's free to check and fix.

Can I use a heat gun to melt ice at the vent termination?

Yeah, you can, just be careful with it. Keep the heat gun on low or medium and keep it moving constantly, don't park it in one spot on the PVC cap or you'll warp it and then you've got a new problem. Honestly, warm water from a kettle poured slowly over the cap does the job just as well and there's zero risk of damaging anything. After you clear it, consider wrapping any exposed exterior pipe sections with foam pipe insulation. That slows down the refreezing significantly. And never use an open flame near a gas appliance vent.

How often should I inspect the Navien vent termination?

At minimum once a year, right before heating season so October or November. If you've already had an E110 from a bird nest, do a spring check too because the same birds absolutely will come back to the same spot. I had one unit that got nested three springs in a row before the homeowner finally put a cage screen over the cap. Takes literally two minutes to walk outside and shine a flashlight at the termination. Way cheaper than an emergency service call at midnight in January when you've got no hot water.

My vent termination is clear but E110 keeps coming back. What now?

If the cap is clean and you can't find a kink in the pipe, calculate the total equivalent feet of your vent run. Every 90-degree elbow adds 5 equivalent feet on top of the actual pipe length. Navien's max for 2-inch PVC is 60 equivalent feet on most models, so do the math. If you're close to or over that, the system's undersized for the run length. The other possibility is the air pressure switch inside the unit is failing. The part itself is usually $40 to $60, but testing and replacing it requires opening the unit, so that's tech territory.

How do I stop E110 from happening every winter?

Three things actually make a permanent difference. First, replace the standard termination cap with a Navien-approved freeze-resistant cap, they're designed to shed ice way better than the stock cap. Second, make sure the condensate drain line runs through a heated space all the way to the floor drain, if any section runs through a cold garage or crawlspace it'll freeze and back up. Third, wrap any exposed vent pipe with foam pipe insulation. Customers who called me every January for years have been quiet since doing all three. It's maybe $80 in parts and an hour of work.

Related Navien Waterheater Error Codes

Code: HUBNavien Tankless Water Heater Error Codes: Complete NPE and NCB Series Guide Code: E773Navien E773 Error Code: Exhaust Overheat Thermal Limit Code: RESETHow to Reset a Navien Tankless Water Heater and Clear Error Codes

Same Fix on Other Brands

Rinnai waterheater63: Rinnai Code 63: Combustion Fan Error

Models Known to Experience E110 Errors

This repair applies to most Navien waterheaters with this error code. Common model numbers include:

NPE-240A, NPE-180A, NPE-210A, NPE-150A, NCB-240E, NCB-180E, NPN-199A, NPE-180S2

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 14, 2026