Navien Error Code 110: What It Means and Safe Next Steps

Rule out an emergency first

If you smell gas, a carbon monoxide alarm sounds, anyone has symptoms of CO exposure, or you see flame, smoke or fire outside the burner area, get everyone out and call 911 from outside. Stay out until officials say it's safe; service comes after that. A code alone cannot determine how urgent a situation is. Stop using a unit with damaged or obstructed venting, scorching or leaking, and arrange qualified service.

Your hot water cuts out, and the Navien display shows 110. A Navien tankless water heater error code 110 directs attention to the air path on the legacy NPE models discussed here. Navien's legacy NPE user manual, including the NPE-240A in our case, labels E110 "Abnormal air pressure." The NFC-H combi boiler manual uses an exhaust-blockage label for the NFC-250/175H and NFC-250/200H. The next questions concern the intake, exhaust, fan and air-pressure sensing. Navien error code 110 doesn't identify a failed part or prove the heat exchanger has failed.

What the code means depends on the model

Error codes are set by each manufacturer, and sometimes by each model family. What a 110 code means differs by brand, so read the label on your unit first and confirm the brand, model and serial number. A Rinnai or Noritz showing a similar number is a different conversation. Within Navien, match the code to the manual for your exact model, because the two manuals linked above describe Navien error code E110 differently. Our Navien error codes guide explains how to record any code before you call.

What you can check for a Navien tankless error code 110

When a Navien 110 error code appears, note the outdoor vent's condition, the weather and any recent work near the vent or heater, such as new siding, a deck or landscaping. You can gather the rest of the evidence without opening the unit:

• Photograph the whole display, including any other codes or icons.
• Record the model and serial number from the rating label without removing a panel.
• From the ground, look at the outside vent terminations for snow, ice, leaves, nests or damage. Don't climb, reach into a termination or remove a screen.
• Note when the code shows up: during hot-water use, at high flow, in wind, after snow or in freezing weather.

Leave the cabinet, vent joints, gas controls, wiring and installer settings alone. If a Navien error 110 returns, stop using the unit and call for model-specific guidance. Don't keep clearing the display to get hot water.

The Hudson case: the code and the damage are separate questions

This guide draws on a documented visit in Hudson, Massachusetts. That Hudson isn't among our 26 directory towns, and this historical case doesn't establish current coverage there. Hudson, New Hampshire, is in the directory, but we don't offer gas appliance work in New Hampshire. We confirm the address, work and availability against our 20-mile Westford service area before booking.

A family had moved into the home and found the hot water inconsistent. The tankless unit, later identified as a 2019 Navien NPE-240A, reportedly cycled on and off. Inspection found white, chalky deposits and corrosion around the sight glass and ignition area. The intake and exhaust were reported about 12 inches apart, with the exhaust ending below or near a porch, and both pipes ran roughly 18 feet vertically in a 16-inch framing bay.

None of those observations proved a cause on its own. Deposits can come from a water leak, condensate, a failed seal or combustion conditions. Whether the vent layout was acceptable depends on the complete NPE-240A instructions, the opening clearances and the porch geometry, and exhaust recirculating under the porch was a possibility to test, not a measured cause.

Heat-exchanger replacement and a Navien warranty claim were pursued. Navien technical support was contacted, and documentation began, including photos of the corrosion and the exterior venting. We don't have a teardown finding, Navien's decision or a completed repair to report, so this case shows how a claim starts, not how it ended.

What a technician checks on the air side

A model-specific diagnosis starts by recording whether the code is current or stored and what the unit was doing when it appeared. Then the intake and exhaust get compared with the appliance instructions: approved material and diameter, total equivalent length after elbows, slope, supports, joints, termination layout and clearances. Common problems include:

• terminations blocked by snow, ice, leaves or nests, or placed where debris collects
• exhaust getting drawn back into the intake in some wind or pressure conditions
• vent material, diameter or fittings the model doesn't allow
• runs longer than the model's equivalent-length limit
• sagging pipe, trapped condensate or separated joints
• screens or guards that aren't approved for the unit
• installer settings that don't match the vent system

The operating side can include fan speed, the air-pressure sensor and its tubing, wiring and the control's response. Nothing gets bypassed to make a code go away, and no smoke or tissue test at the termination replaces the manufacturer's procedure.

Why code 110 doesn't prove heat-exchanger failure

A heat exchanger moves burner heat into the water, while error code 110 starts with the air path. The two interact during combustion, but a restricted vent can disrupt operation without damaging the exchanger, and an exchanger or seal can leak without causing an airflow code. Deposits like the ones in Hudson justify a close look at leaks, condensate, seals and combustion. A new exchanger installed without fixing a vent, water, condensate, gas or control problem can leave the root cause in place.

Whether to repair or replace depends on the damage found, parts availability, warranty status and the cost of the full correction, not the unit's age alone. Our guide to Navien heat exchanger replacement in Lowell covers what happens once an exchanger replacement is confirmed.

Warranty: what the heat-exchanger term covers

Navien's legacy NPE-A warranty table lists a 15-year heat-exchanger term for qualifying residential standard or controlled-recirculation applications; other applications carry shorter terms. Eligibility depends on the exact model, serial number, application, installation, registration or proof requirements, maintenance, water conditions and the current written terms, and Navien makes the decision. A heat-exchanger term isn't a whole-unit warranty. Labor, diagnosis, venting corrections and connected work may fall outside it, and the code alone doesn't establish a claim.

Water testing is a separate question

The Hudson notes recorded water pressure above 60 psi and concluded water quality wasn't involved. Pressure isn't water chemistry, though. When deposits or scale are present, tests for hardness, pH, iron, total dissolved solids and other relevant parameters help assess the water conditions. They don't prove what caused a particular failure. Our water testing service supplies that evidence alongside the equipment inspection; it doesn't replace the air-path diagnosis for code 110.

Getting a model-specific diagnosis

Jeneral Plumbing is owner-operated by a Licensed Master Plumber (MA #9628831-PL-M) with 20+ years in the trade, including seven with a gas utility, factory trained by Navien and Navien Service Specialist (NSS) certified. That supports model-specific diagnosis; it doesn't make us Navien's warranty decision-maker. We're based in Westford, MA, and serve homes within 20 miles across Middlesex & Worcester County. Our gas appliance work is Massachusetts-only, and we confirm your address, the work and availability when you call. During regular hours, a visit carries an $80 dispatch fee — the cost of the visit, waived when you hire us for the work. Repairs are priced at a flat rate for your approval before work begins. Call (978) 392-7789 with a photo of the display and the model number, or see our tankless water heater service.

Can I reset a Navien code 110 myself?

There isn't a reset procedure that fits every Navien model. Photograph the display, identify the exact model and ask for guidance based on its owner manual. Because this code concerns combustion air or exhaust on the models above, repeatedly resetting it can keep an unresolved fault in use. If the code returns, leave the unit off. For a gas smell or CO alarm, leave the building and call 911 from outside; service follows once officials clear the home.