Navien Tankless Water Heater Error Code 110-01: What It Means & How

You step into the shower, ready for a rush of hot water, but instead, you’re met with a lukewarm drizzle. A quick check of your Navien unit reveals a blinking light and a cryptic message: navien tankless water heater error code 110-01. It’s a frustrating moment that can throw off your entire day.

I get it. As a technician, I’ve seen that look of confusion on a homeowner’s face dozens of times. But here’s the good news: you’ve come to the right place. I promise to demystify this specific error code for you. We’re not going to use confusing jargon; we’re going to talk like two people standing in front of the unit together.

In this complete guide, we’ll walk through what error code 110-01 actually means, explore its common causes, and provide a safe, step-by-step troubleshooting process you can follow. You’ll learn exactly what you can check yourself and, just as importantly, when it’s time to call for backup. Let’s get that hot water flowing again.

What Exactly is Navien Error Code 110-01?

Think of error codes as your water heater’s way of telling you what’s wrong. They can be intimidating, but they’re actually incredibly helpful diagnostic tools.

The navien tankless water heater error code 110-01 specifically points to an “Abnormal Outdoor Temperature Sensor.”

In simple terms, your Navien unit has a small sensor that measures the temperature of the air being pulled in from outside for combustion. This sensor is vital for high-efficiency condensing units like Navien’s. It helps the main control board—the “brain” of the heater—adjust the burning process to be as efficient as possible, saving you money on your gas bill.

When you see error 110-01, the control board is saying one of three things:

The sensor is reading a temperature that is way too high or way too low for safe operation.
The sensor itself has failed and is sending a bad signal.
The connection between the sensor and the control board has been lost.

The unit then enters a “lockout” mode to protect itself from potential damage. Don’t worry—this is a safety feature working as designed. Our job is to figure out why it was triggered.

Common Problems Behind the 110-01 Fault Code

Before we touch anything, let’s understand the usual suspects. Knowing the potential causes makes troubleshooting much more effective. This is one of the most important navien tankless water heater error code 110-01 tips I can give you: diagnose before you act.

A Faulty or Damaged Sensor

This is the most frequent culprit. The outdoor temperature sensor, also known as a thermistor, is a small electronic component. Like any part, it can simply fail over time. It can also be damaged by moisture, corrosion, or physical impact, leading it to send incorrect readings to the control board.

Loose or Damaged Wiring

The sensor is connected to the main control board by a pair of wires. Over time, vibrations from the unit can cause these connections to become loose. In other cases, pests might chew on the wires, or corrosion could build up on the connection points, interrupting the signal. A broken wire means a broken line of communication.

Environmental Blockages

Sometimes, the sensor is working perfectly, but its environment is fooling it. If the air intake vent is blocked by a snowdrift, a pile of leaves, or even a dryer vent blowing hot, moist air directly at it, the sensor will read an extreme temperature. This is a classic example of one of the common problems with navien tankless water heater error code 110-01 that isn’t a component failure.

A Control Board Glitch

This is the least common cause, but it does happen. On rare occasions, the sensor and wiring are fine, but the main control board (PCB) is misinterpreting the data. This is a more complex issue that almost always requires a professional diagnosis.

Your Step-by-Step Guide to Troubleshooting Error Code 110-01

Alright, let’s get our hands dirty—safely. This navien tankless water heater error code 110-01 guide will walk you through the checks you can perform without needing special tools. Follow these steps in order.

Safety First: Before you open any panels on your water heater, you must disconnect the electrical power to the unit. You can do this by unplugging it from the wall outlet or by switching off the corresponding breaker in your home’s electrical panel.

Step 1: The Simple Power Cycle (The “Reboot”)

Electronics can sometimes experience temporary glitches. The first and easiest step is to simply reboot the water heater.

Turn off the electrical power to the unit.
Wait for at least 60 seconds. This allows the internal capacitors to fully discharge and the memory to clear.
Restore power to the unit.

Listen for the unit to cycle on. If the error code disappears and your hot water returns, it may have just been a momentary glitch. If the error code comes back, proceed to the next step.

Step 2: Visually Inspect the Air Intake and Sensor Area

Now, let’s check the environment around your unit. No need to open anything up just yet.

Check the Vents: Go outside and look at your unit’s intake and exhaust vents (usually two white PVC pipes). Are they blocked by leaves, snow, bird nests, or other debris? Is a nearby dryer vent blowing onto them? Clear away any obstructions.
Locate the Sensor: The outdoor temperature sensor is typically located right inside the air intake pipe or on the air inlet collar inside the unit’s cabinet. You may be able to see it just by looking into the intake pipe from the outside.

Step 3: Inspect the Sensor and Wiring (Power OFF!)

If the external inspection didn’t reveal anything, it’s time for a closer look inside. Remember to ensure the power is disconnected before proceeding.

Remove the front cover of your Navien unit. This is usually held on by a few screws at the bottom.
Locate the outdoor temperature sensor. It’s a small probe with two wires coming out of it, typically near the air intake assembly. Your user manual will have a diagram to help you pinpoint its exact location.
Check for Obvious Damage: Look closely at the sensor. Do you see any signs of burning, melting, or physical damage?
Check the Wires: Follow the wires from the sensor back to where they connect to a wiring harness or the control board. Are the wires frayed, broken, or discolored from corrosion? Gently tug on the connectors to ensure they are seated firmly. A loose connection is a very common find.

If you find a loose wire and can securely reconnect it, you may have just solved the problem. If you see obvious damage to the sensor or wires, that part will need to be replaced.

When to Put Down the Tools and Call a Navien Pro

Knowing your limits is the most important part of any DIY project. While the steps above are safe for most homeowners, there are clear signs that it’s time to call a qualified technician.

You should call a professional if:

You’ve completed all the steps above and the error code persists.
You see signs of burnt wires, a damaged control board, or anything that makes you uncomfortable.
The problem requires a multimeter to test the sensor’s resistance (Ohm reading). This is a definitive test but requires the right tool and knowledge.
You suspect the main control board is the issue. Replacing a control board is a complex job that should only be done by a trained technician.

The benefits of calling a pro for this error code are significant. They can diagnose the issue with 100% certainty, have the correct replacement parts on their truck, and ensure the repair is done safely and correctly, preserving your unit’s warranty.

Navien Tankless Water Heater Error Code 110-01 Best Practices for Prevention

An ounce of prevention is worth a pound of cure. Following a simple navien tankless water heater error code 110-01 care guide can help you avoid seeing this error in the first place.

Perform Regular Visual Inspections

Once a season, take a quick walk around your unit. Make sure the intake and exhaust vents are clear of vegetation, snow, and debris. This simple five-minute check can prevent a world of headaches.

Schedule Annual Professional Maintenance

This is the single most effective thing you can do. During an annual service, a technician will clean and inspect all components, including sensors and wiring connections. They can spot a corroding sensor or a loose wire long before it triggers a fault code. This not only improves reliability but also ensures your unit runs at peak efficiency, making it a more sustainable and eco-friendly choice.

Frequently Asked Questions About Navien Error Code 110-01

Can I still use my water heater with error code 110-01?

No. Error code 110-01 is a “hard lockout,” which means the unit will not operate until the fault is cleared. This is a safety measure to prevent the unit from running in a potentially unsafe or inefficient condition.

How much does it cost to fix error code 110-01?

The cost can vary widely. If a simple reset or clearing a blocked vent fixes it, the cost is $0. If the outdoor temperature sensor needs to be replaced, you can expect to pay between $150 and $350 for the part and professional labor. If the issue is the main control board, the repair could be significantly more expensive.

Can I just bypass the outdoor temperature sensor?

Absolutely not. You should never attempt to bypass any safety sensor on a gas appliance. The outdoor temperature sensor is crucial for the efficient and safe operation of your condensing water heater. Bypassing it could lead to poor performance, damage to the unit, and create a dangerous situation. It will also void your warranty.

Facing an error code on your Navien unit can be stressful, but you’re now equipped with the knowledge to tackle it. By following the simple troubleshooting steps in this guide, you can often identify and sometimes even resolve the issue yourself. Most importantly, you now know how to perform these checks safely and recognize when it’s time to bring in a professional.

A little bit of maintenance and understanding go a long way in keeping your home’s systems running smoothly. You’ve got this! Stay safe and enjoy that 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.