Navien Tankless Water Heater 598 Error Code - A Pro'S Guide To Fixing

That sinking feeling hits you the moment you step into the shower. You turn the handle, expecting a rush of comforting hot water, but all you get is an icy surprise. A quick trip to your Navien unit reveals the source of your trouble: a blinking display with the navien tankless water heater 598 error code.

It’s frustrating, confusing, and immediately brings your daily routine to a halt. But don’t worry—we’re here to help you decipher this code and get your hot water flowing again.

I’m an HVACR technician, and I’ve seen this error plenty of times in the field. While it sounds technical, understanding it is the first step to a solution. We promise this guide will walk you through what the 598 error means, what causes it, and provide a safe, step-by-step plan to troubleshoot it.

In this comprehensive navien tankless water heater 598 error code guide, you’ll learn the simple reset procedure, safe visual checks you can perform yourself, and the critical signs that tell you it’s time to call a qualified professional. Let’s get that hot water back on!

What Does the Navien 598 Error Code Actually Mean?

First things first, let’s translate what your water heater is trying to tell you. The official Navien manual defines Error Code 598 as an “Abnormal Gas Valve Operation” issue. In simple terms, the unit’s main brain—the printed circuit board (PCB)—has detected a problem with the signal it’s sending to, or receiving from, the gas valve.

Think of it like a conversation between a manager (the PCB) and an employee (the gas valve). The manager gives a command, but the employee either doesn’t respond correctly or the manager can’t confirm the command was received. When this communication breaks down, the system shuts down for safety.

This is a crucial safety feature. The last thing you want is a gas valve operating unpredictably. The 598 error code is your Navien’s way of saying, “Hold on, something isn’t right with the gas system’s electronics, so I’m stopping until it’s checked.”

Uncovering the Common Problems with Navien Tankless Water Heater 598 Error Code

While the error points to a communication breakdown, several culprits could be causing the issue. From my experience, the problem usually falls into one of three categories. Understanding these common problems will help you narrow down the source.

A Faulty Main Control Board (PCB)

The PCB is the electronic heart of your Navien water heater. It controls every function, from igniting the burner to modulating the gas flow. Over time, electronic components can fail. The board might send an erratic signal to the gas valve or fail to correctly interpret the feedback it receives, triggering the 598 error even if the gas valve itself is perfectly fine.

Issues with the Gas Valve Itself

The gas valve is an electromechanical part that opens and closes to allow gas to flow to the burner. The electronic solenoid that controls this action can fail, or the internal components can become stuck. While less common than a PCB issue for this specific code, a failing gas valve is a definite possibility and a major safety component.

Loose or Damaged Wiring Harness

This is one of the most common—and fortunately, easiest to fix—causes. The wiring harness is the bundle of wires that connects the PCB to the gas valve. Vibrations from normal operation, moisture, or even a factory defect can cause these connections to become loose. A poor connection creates an unreliable signal, which the PCB immediately flags as an error.

Your Step-by-Step Navien Tankless Water Heater 598 Error Code Guide

Alright, let’s walk through a few safe checks you can perform. This is your practical, how to navien tankless water heater 598 error code action plan. Before you begin, please read this safety warning carefully.

CRITICAL SAFETY WARNING

Your Navien unit involves electricity, natural gas or propane, and water. Before opening the front panel of your water heater for any reason, you MUST turn off the power to the unit at your home’s circuit breaker. If you are not 100% confident and comfortable with these steps, your safety is more important than a cold shower. Please call a licensed technician.

Step 1: The Simple Reset (The First and Easiest Fix)

Sometimes, a temporary power surge or a momentary electronic glitch can cause a false error code. The first step is always the simplest: a power cycle reset.

Locate the electrical cord for your Navien unit and unplug it from the wall outlet.
Wait for at least 60 seconds. This allows the internal capacitors on the control board to fully discharge and clear any temporary memory glitches.
Plug the unit back in firmly.
Turn on a hot water tap and see if the unit operates normally.

If the error clears and doesn’t return, you may have just experienced a one-time glitch. However, if the navien tankless water heater 598 error code comes back immediately or within a few hours, it’s a clear sign of a persistent problem that needs further investigation.

Step 2: Visual Inspection of Wiring (For the Confident DIYer)

If the reset didn’t work, the next step is to check for the most common culprit: a loose wire. Remember our safety warning!

Turn off power at the circuit breaker. Double-check that the unit’s display is completely blank and has no power.
Remove the screws holding the front cover of your Navien unit and set it aside carefully.
Locate the main control board (PCB). It’s typically a green board with many wires connected to it.
Locate the gas valve. It’s usually a metal block near the bottom of the unit where the gas line connects, with a few wires leading to it.
Follow the wires from the gas valve back to the PCB. This is the wiring harness we need to inspect. Look for a multi-pin plastic connector.
Gently but firmly, push on the connector at the PCB and the connector at the gas valve to ensure they are fully seated. Sometimes, they can wiggle loose just enough to cause a bad connection.
Visually inspect the wires for any signs of damage, such as being pinched, frayed, or showing signs of corrosion or burning.
If everything looks secure and undamaged, replace the front cover and restore power at the breaker to see if the issue is resolved.

This simple check is one of the most valuable navien tankless water heater 598 error code tips a technician can offer, as it often solves the problem without needing any replacement parts.

When to Stop and Call a Licensed Navien Technician

Knowing your limits is the most important part of any DIY project. The 598 error code involves the two most critical systems in your water heater: electricity and gas. If the steps above didn’t solve your problem, it’s time to call a professional. No exceptions.

Call a pro immediately if:

The reset and wiring check did not fix the error.
You smell even the faintest odor of gas. If you do, leave the area immediately, call your gas company from a safe distance, and then call an HVACR technician.
You are not completely comfortable opening the unit’s cover or working around its components.
The error code keeps coming back intermittently. This points to a component that is actively failing and needs to be replaced before it fails completely.

A qualified technician will use a multimeter to perform advanced diagnostics. They will test the voltage output from the PCB, check the resistance (ohms) of the gas valve solenoid, and systematically determine which component is faulty. This is not something that can be done without proper tools and training.

Best Practices: Preventing Future Navien Error Codes

Once your hot water is back, you’ll want to keep it that way. Following a good navien tankless water heater 598 error code care guide is key to reliability. Adopting these best practices will not only help prevent the 598 error but also extend the life of your entire unit, making it a more sustainable navien tankless water heater 598 error code solution.

The Importance of Annual Maintenance

Your tankless water heater is a complex machine that works hard every day. Annual professional maintenance is the single best thing you can do for it.

System Flushing (Descaling): Hard water minerals build up inside the heat exchanger, forcing the unit to work harder. This extra stress can shorten the lifespan of all components, including electronics.
Proactive Inspections: During a tune-up, a technician will inspect all wiring connections, check for signs of wear and tear, and clean essential components. They can often spot a potential problem long before it triggers an error code.

Install a High-Quality Surge Protector

The PCB is highly sensitive to electrical fluctuations. Power surges from storms or instability in the grid can damage it. Plugging your Navien unit into a dedicated, high-quality surge protector is a small investment that can save you from a very expensive PCB replacement down the road.

Keep the Area Around the Unit Clear

Ensure your water heater has plenty of space around it for proper ventilation. Don’t store chemicals, laundry supplies, or flammable items nearby. Keeping the area clean prevents dust and debris from being pulled into the unit, promoting better and more eco-friendly navien tankless water heater 598 error code prevention through efficient operation.

Frequently Asked Questions About the Navien 598 Error Code

Can I fix the Navien 598 error code myself?

You can safely perform the basic troubleshooting steps of a power reset and a visual inspection of the wiring harness (with the power OFF). However, any steps that require testing or replacing components like the gas valve or PCB must be performed by a licensed and qualified technician due to the risks associated with gas and electricity.

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

The cost can vary significantly based on the cause. If it’s simply a loose wire that a technician tightens, you may only pay for the service call fee. If the main control board (PCB) or the gas valve assembly needs to be replaced, you can expect the cost to be several hundred dollars for parts and labor.

Is the 598 error code dangerous?

The error code itself is a safety mechanism designed to prevent a dangerous situation. It shuts the unit down because it has detected an abnormality in the gas valve control system. The underlying cause could be hazardous if left unaddressed, which is why it’s critical to resolve the issue and not simply keep resetting the unit.

Does this error have anything to do with water hardness or needing a flush?

Not directly. The 598 error is purely electrical and relates to the communication between the control board and the gas valve. However, neglecting maintenance like system flushing puts a heavy strain on the entire water heater. This added stress and heat can contribute to the premature failure of electronic components over the long term.

Dealing with a navien tankless water heater 598 error code can be a major headache, but you’re now equipped with the knowledge to approach it logically and safely. Remember the key takeaways: first, try a simple reset. Second, if you’re comfortable, perform a careful visual inspection of the wiring with the power off. And third, know when to stop and call for professional help.

Your safety is always the top priority. By following these steps, you can confidently diagnose the situation and take the right action to get your reliable, on-demand hot water back. Stay safe and stay comfortable!

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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.