Navien Hot Water Heater Error 110 – A Pro’S Guide To Diagnosing

There’s nothing quite like the jolt of an unexpectedly cold shower. You were expecting a relaxing, steamy stream of hot water, but instead, you get an icy surprise. You head to your Navien tankless unit, only to see a cryptic message flashing on the display: Error 110. It’s a frustrating moment, but don’t worry—we see this all the time.

I promise, we can get to the bottom of this together. The navien hot water heater error 110 is one of the most common codes a homeowner will encounter, and it’s often related to issues you can safely investigate and sometimes even fix yourself.

In this complete guide from HVACRLY, we’ll act as your virtual technician. We’ll break down what Error 110 actually means, walk you through the most common causes, and provide a safe, step-by-step troubleshooting checklist. You’ll learn exactly what you can do and, just as importantly, when it’s time to call in a professional for backup. Let’s get that hot water flowing again.

What Exactly Is Navien Error Code 110?

First things first, let’s decode the message. When your Navien unit displays Error 110, it’s signaling an “Abnormal Exhaust Temperature” or “Exhaust Overheat” fault. In simple terms, a sensor inside your water heater has detected that the exhaust gases leaving the unit are dangerously hot.

Think of this not as a failure, but as a critical safety feature doing its job perfectly. The water heater’s main control board immediately shuts down the burner to prevent damage to sensitive internal components, like the heat exchanger, and to ensure your home remains safe. The heat isn’t being transferred to the water correctly, so it’s getting trapped in the exhaust.

Our job now is to figure out why that heat is getting trapped. This is the first step in our practical navien hot water heater error 110 guide.

The Common Culprits: Uncovering the Root Causes of Error 110

From my experience in the field, Error 110 almost always traces back to an issue with either airflow or water flow. Heat needs to be able to escape through the exhaust, and it needs to be absorbed by the water. When one of these processes is hindered, you get an overheat condition. Let’s look at the most common problems with navien hot water heater error 110.

Blocked Venting or Intake Pipes

This is, by far, the number one cause. Your high-efficiency Navien heater needs to breathe. It pulls in fresh air for combustion (intake) and pushes out exhaust gases (vent). If either of these pipes is blocked, the unit can’t operate correctly.

Common blockages include:

Birds’ nests, hornet nests, or other debris inside the vent termination cap.
Snow, ice, or frost covering the pipes in the winter.
Leaves, mulch, or overgrown shrubs blocking the pipes outside your home.
Improperly sloped vent pipes that allow condensation to pool and block airflow.

Scale Buildup in the Heat Exchanger

If you live in an area with hard water, this is a major suspect. Hard water contains dissolved minerals like calcium and magnesium. Over time, these minerals precipitate out of the water and form a hard, crusty layer—known as scale—on the inside of the heat exchanger.

This scale acts like a layer of insulation. It prevents heat from efficiently transferring from the burner to your water. The burner keeps firing, but the heat has nowhere to go, causing the exhaust temperature to skyrocket and triggering Error 110. This is a primary focus of any good navien hot water heater error 110 care guide.

A Failing Recirculation System

Some Navien models have an internal recirculation pump designed to provide “instant” hot water. If this pump or its associated flow sensor fails, water won’t move through the main heat exchanger quickly enough. The result is the same: the water can’t absorb the heat fast enough, leading to an overheat fault.

Issues with the Condensate Drain

As a high-efficiency condensing unit, your Navien produces acidic water (condensate) as a byproduct of combustion. This water must drain away through a small tube. If this drain line becomes clogged with debris or freezes, the condensate can back up into the unit, potentially affecting sensors and causing a variety of error codes, including Error 110.

Your Safe DIY Troubleshooting Guide for Navien Hot Water Heater Error 110

Alright, let’s roll up our sleeves and do some safe investigating. Before you touch anything, please read this carefully.

SAFETY FIRST: Your safety is the top priority. Before performing any checks that involve more than just looking, you must turn off the electrical power to the water heater at your home’s circuit breaker panel. If you are ever unsure, uncomfortable, or smell gas, stop immediately and call a licensed HVAC or plumbing professional. This is one of the most important navien hot water heater error 110 tips we can offer.

Here is how to navien hot water heater error 110 troubleshoot safely:

Perform a Thorough Visual Inspection Outside: Go to where your PVC vent pipes exit your home. Carefully inspect the intake and exhaust pipe terminations. Is there a bird’s nest in the screen? Is a snowdrift covering the pipes? Are bushes growing too close? Clear away any and all obstructions. This simple step solves the problem more often than you’d think.
Reset the Unit (The Right Way): Once you’ve cleared any external blockages, it’s time for a reset. Don’t just press the power button on the unit. Go to your circuit breaker and flip the breaker for the water heater off. Wait a full five minutes to allow all the capacitors on the control board to discharge. Then, flip the breaker back on. This hard reset is more effective than just using the front panel.
Check the Condensate Line: Locate the small, often clear or white, plastic tube coming from the bottom of your Navien unit. It should be sloped downwards towards a floor drain or condensate pump. Check for any kinks, clogs, or visible water backed up in the line. If it’s clogged, you may be able to gently clear it to restore proper drainage.
Review Your Maintenance History: Be honest—when was the last time the unit was professionally serviced or descaled? If it has been more than a year (or six months in very hard water areas), then scale buildup is the most likely culprit if the vents are clear. This is a strong clue that it’s time for maintenance.

Advanced Checks & When to Call a Navien Pro

If the simple checks above didn’t resolve the error, the problem is likely internal. This is where the line between DIY and professional work becomes very clear.

The Descaling Process (For the Confident DIYer)

Descaling, or flushing, the unit is the solution for scale buildup. This involves using an isolation valve kit, a small utility pump, a bucket, and a descaling solution (food-grade white vinegar is a great eco-friendly navien hot water heater error 110 solution) to circulate the cleaner through the heat exchanger. While many homeowners can do this, it requires specific equipment and a careful procedure. If you’re not 100% confident, it’s best left to a pro.

Signs You Need to Stop and Call for Help

It’s crucial to know your limits. Call a qualified technician immediately if:

The navien hot water heater error 110 returns immediately after a reset, even with clear vents.
You hear loud or unusual noises like rumbling, banging, or a “kettling” sound.
You are not comfortable with the descaling process or don’t have the right tools.
You suspect the issue is an internal component like a sensor, fan, or pump.
You have completed all the safe DIY steps and the problem persists.

A professional technician has the tools and training to test gas pressure, check sensor resistance with a multimeter, and safely inspect the internal burner and heat exchanger assembly—tasks that should never be attempted by an untrained individual.

Best Practices for Preventing Error 110 in the Future

The best way to fix a problem is to prevent it from happening in the first place. Following these navien hot water heater error 110 best practices will dramatically reduce the chances of seeing that code again and extend the life of your investment.

Schedule Annual Professional Maintenance

This is non-negotiable for tankless water heaters. An annual service call from a qualified technician is the single most important thing you can do. They will thoroughly inspect the venting, clean all necessary components, and perform a full descaling service. This ensures efficiency, safety, and reliability.

Consider a Water Softener

If you live in an area with hard water, a whole-home water softener is one of the best investments you can make. It protects not just your Navien unit, but also your dishwasher, washing machine, faucets, and showerheads from the damaging effects of scale buildup. This is a key part of any long-term, sustainable navien hot water heater error 110 prevention plan.

Keep Vents Clear Year-Round

Make it a habit. After a big snowstorm, clear the vents. In the spring, check for nests. In the fall, make sure leaves aren’t piling up against them. A few minutes of prevention can save you a service call and a cold shower.

Frequently Asked Questions About Navien Error 110

Can I just keep resetting my Navien heater if I get Error 110?

No, this is a very bad idea. While a reset might temporarily clear the code, it does absolutely nothing to fix the underlying problem causing the overheat. Continually forcing the unit to run in an unsafe condition can lead to permanent, catastrophic damage to the heat exchanger, which is the most expensive part of the water heater.

How much does it cost to fix a Navien Error 110?

The cost can range from $0 to over $1,500. If the cause is a blocked vent that you clear yourself, it’s free. If it requires a professional service call for a standard descaling, you might expect to pay between $250 and $500. However, if the error was ignored and caused damage to a major component like the main control board or heat exchanger, the repair cost could easily exceed $1,000.

Is Navien Error 110 dangerous?

The error code itself is a safety feature that is preventing a dangerous situation. It’s doing its job by shutting the unit down. The underlying cause, however, could be hazardous if left unaddressed. For example, a completely blocked exhaust vent could potentially lead to a buildup of carbon monoxide (CO) in your home if the safety systems were to fail. This is why you must never ignore this error or try to bypass the safety controls.

Tackling an error code on your Navien heater can feel intimidating, but you’ve taken the first and most important step by seeking out reliable information. By following the safe checks in this guide, you can confidently identify simple issues and know exactly when it’s time to call for professional backup. Remember to prioritize safety above all else.

Stay safe, stay informed, and enjoy that wonderfully consistent hot water!

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David Clark

Founder & Lead HVAC Specialist at HVACRLY

David Clark is the founder of HVACrly and a certified HVAC specialist with 10+ years working on residential and light-commercial systems. He turns complex heating, cooling, ventilation, and refrigeration topics into clear, actionable guides focused on safety and energy efficiency. When he’s not on a service call, he’s testing tools and writing step-by-step tutorials.