Navien Water Heater Error 598 - Your Complete Guide To Fixing It Fast

There’s nothing quite like the jolt of an icy shower when you were expecting a warm, relaxing stream. You rush to your Navien tankless water heater, only to be greeted by a blinking, cryptic message: Error Code 598. It’s a moment of frustration every homeowner dreads, leaving you wondering what went wrong and how long you’ll be without hot water.

We get it. At HVACRLY, we’ve seen this exact scenario play out in countless homes. That feeling of helplessness when a crucial appliance stops working is universal. But here’s the good news: you’ve come to the right place.

We promise this guide will demystify the navien water heater error 598, turning your confusion into confidence. We’re going to walk you through exactly what this error means, what causes it, and the safe, practical steps you can take to troubleshoot it yourself—just like a seasoned technician would.

In this article, you’ll discover the simple visual checks that solve the problem most of the time, learn to identify when it’s time to call a professional for your safety, and understand the best practices to prevent this error from ever coming back. Let’s get that hot water flowing again.

What Exactly Is Navien Error Code 598?

First things first, let’s translate what your water heater is trying to tell you. In the simplest terms, Error Code 598 means “Abnormal Exhaust Temperature.”

Your Navien tankless water heater is a high-efficiency machine. It works by using a powerful burner to heat water as it flows through a component called a heat exchanger. As part of this process, it produces hot exhaust gases that must be safely vented outside your home.

A special sensor, the exhaust temperature sensor, constantly monitors the temperature of these gases. If that temperature climbs above a safe, pre-set limit, the system’s brain—the control board—triggers Error 598 and immediately shuts the unit down.

Think of it as a very smart safety feature. It’s not just a random glitch; it’s your water heater protecting itself from overheating, which could damage sensitive internal components and, more importantly, create a potential safety hazard. This is one of the key benefits of navien water heater error 598—it acts as a guardian for your system and your home.

The Root Causes: Why Is My Navien Showing Error 598?

So, why would the exhaust get too hot in the first place? The issue almost always boils down to one thing: improper airflow or heat transfer. When heat can’t escape the unit efficiently, it builds up and triggers the sensor. Here are the most common problems with navien water heater error 598 that we see in the field.

1. Blocked Venting or Exhaust Pipe

This is, by far, the most frequent culprit. Your Navien needs to breathe out. If the exhaust vent is obstructed, hot gases get trapped inside the unit, causing the temperature to spike.

Common blockages include:

Bird nests, wasp nests, or other debris in the vent termination cap.
Heavy snow, ice, or overgrown landscaping covering the exterior vent.
A sagging vent pipe that has created a low point where condensation can pool and block airflow.

2. Restricted Air Intake

Just as it needs to breathe out, your water heater needs to breathe in. It requires a steady supply of fresh air for proper combustion. If the air intake pipe is blocked, the fuel-to-air mixture becomes too rich, leading to incomplete combustion and higher exhaust temperatures.

3. Severe Mineral Scale Buildup in the Heat Exchanger

If you live in an area with hard water, minerals like calcium and magnesium can build up inside the heat exchanger over time. This layer of scale acts like an insulator, preventing heat from transferring efficiently to the water.

The burner keeps firing, trying to heat the water, but the heat has nowhere to go. It gets trapped and sent up the exhaust flue, causing the temperature to skyrocket and trigger Error 598.

4. A Faulty Exhaust Temperature Sensor

Sometimes, the problem isn’t with the temperature itself but with the sensor reporting it. Like any electronic component, these sensors can fail over time. It might be sending an incorrect, high-temperature reading to the control board, causing a shutdown even when everything else is fine.

Your Step-by-Step Navien Water Heater Error 598 Guide for DIY Troubleshooting

Alright, let’s roll up our sleeves. Before you pick up the phone to call for service, there are a few safe and simple checks you can perform. This section is your essential guide on how to navien water heater error 598 safely.

A Quick Safety Warning: We will only be covering visual inspections and basic resets. Do not attempt to open the water heater’s main cover or handle any gas or electrical components unless you are a qualified technician. Your safety is paramount.

Perform a Simple Power Cycle
The oldest trick in the tech support book often works. Sometimes, a temporary glitch can cause a false error. Unplug your Navien unit from the wall outlet, wait a full 60 seconds to allow the internal capacitors to discharge, and then plug it back in. This simple reset can sometimes clear the code if it was a one-time fluke.
Inspect the Exterior Vent Terminations
Go outside to where your PVC vent pipes exit your home. Carefully inspect the intake (air in) and exhaust (air out) pipes. Look for any visible obstructions. Are there leaves, grass clippings, or a pesky bird’s nest blocking the screen? Is a nearby bush pressing against it? In the winter, is it blocked by snow or ice? Clear away any debris you find.
Check the Condensate Drain Line
High-efficiency appliances like your Navien produce condensation, which is drained away through a small tube. If this line gets clogged with sediment or frozen, the backup can interfere with the system’s operation and sometimes contribute to pressure issues that lead to overheating. Ensure the tube is clear and draining properly.
Listen for Unusual Noises
When you try to run the hot water, listen to the unit. Do you hear a rumbling or “kettling” sound? This is a classic sign of severe scale buildup inside the heat exchanger. If you hear this, the problem is internal, and it’s time to stop troubleshooting and call a professional for a system flush.

When to Put Down the Tools: Calling a Professional for Error 598

The DIY checks above are great first steps, but it’s crucial to know your limits. This is one of the most important navien water heater error 598 tips we can offer: don’t risk your safety or damage your equipment.

It’s time to call a licensed HVACR technician if:

The error code returns immediately after a reset and you’ve confirmed the vents are clear.
You suspect the issue is mineral scale (e.g., you hear kettling noises or live in a hard water area and the unit has never been serviced).
You need to check internal components like the exhaust sensor, burner, or internal vent piping.
You are not 100% comfortable performing any of the steps listed above.

A professional has the right tools, like a manometer to check gas pressure and a multimeter to test sensors, and the training to safely diagnose and repair the root cause. Attempting to service the internal components yourself can be dangerous and may void your warranty.

A Proactive Navien Water Heater Error 598 Care Guide

The best way to deal with Error 598 is to never see it in the first place. Following a few navien water heater error 598 best practices can dramatically improve your unit’s reliability and efficiency.

The Critical Importance of Annual Flushing

This is the single most important maintenance task for any tankless water heater. An annual descaling or “flushing” service involves circulating a special solution (usually vinegar-based) through the heat exchanger to dissolve mineral buildup before it becomes a problem.

This not only prevents Error 598 but also ensures your unit runs at peak efficiency, saving you money on energy bills. A well-maintained unit is a more sustainable navien water heater error 598 solution, as it uses less energy and lasts longer, reducing waste. This is the cornerstone of an eco-friendly navien water heater error 598 prevention plan.

Keep Vents Clear Year-Round

Make a habit of checking your exterior vents every few months. Trim back any plants that are getting too close and be mindful of snow accumulation during the winter. A simple visual check is all it takes.

Frequently Asked Questions About Navien Water Heater Error 598

Can I just keep resetting my Navien when I get error 598?

No, this is a very bad idea. The error code is a safety alert. By repeatedly resetting it, you are ignoring the underlying problem and forcing the unit to run in an unsafe condition. This can lead to costly damage to the heat exchanger or other critical components.

How much does it cost to fix a Navien error 598?

The cost can vary widely. If the fix is simply clearing a blocked vent, it might just be the cost of a service call. If the heat exchanger needs to be professionally descaled, you can expect to pay a few hundred dollars. If a part like the temperature sensor has failed, the cost will include the part plus labor.

Is hard water the main cause of error 598?

It’s one of the two main causes, alongside blocked venting. In areas with very hard water, scale buildup is an almost guaranteed problem if the unit isn’t flushed annually. If your vents are perfectly clear, scale is the next likely suspect.

Your Path Back to Hot Water

Dealing with a navien water heater error 598 can feel daunting, but it doesn’t have to be. By understanding that it’s a safety signal about high exhaust temperatures, you’re already halfway to solving the problem.

Remember the key takeaways from our guide: start with the simple, safe visual checks of your vents, never ignore the error by repeatedly resetting the unit, and recognize that annual maintenance is the ultimate key to prevention. A professional flush is not an expense; it’s an investment in your water heater’s longevity and efficiency.

You have the knowledge to tackle the initial steps with confidence. For everything else, your local HVACR pro is ready to help. Stay safe, stay informed, and get ready to enjoy that wonderfully consistent hot water once again!

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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.