Error 353 On Navien Tankless Water Heater - Your Complete DIY

There’s nothing quite like the jolt of an unexpectedly icy shower to ruin your morning. You head over to your Navien tankless water heater, and there it is: a blinking, cryptic message. If you’re seeing error 353 on your Navien tankless water heater, you’re probably feeling a mix of confusion and frustration. I get it completely. In my years as an HVACR technician, I’ve seen this code pop up many times.

But here’s the good news: don’t panic. This error code is actually your unit’s way of protecting itself and your home from potential water damage. It’s a warning, not a death sentence for your heater.

I promise this guide will walk you through exactly what this error means, what causes it, and the safe, step-by-step checks you can perform yourself. We’ll explore everything from simple fixes to understanding when it’s time to call in a professional, giving you the confidence to tackle this issue head-on.

Let’s get that hot water flowing again. Together, we’ll decode this error and find the right solution.

What Exactly is Error Code 353 on a Navien Unit?

First things first, let’s translate what your Navien is trying to tell you. Error 353 is a “Wet Leak Sensor” error. Inside the cabinet of your highly efficient water heater, there’s a small, vigilant sensor sitting at the very bottom.

Its only job is to detect the presence of moisture. If even a small amount of water pools up and touches this sensor, it immediately triggers the error code and shuts down the unit’s operation. This is a critical safety feature designed to prevent a small drip from turning into a major, damaging leak inside your home.

So, when you see Error 353, your first thought shouldn’t be that your heater is broken. Instead, think of it as a successful alert. The system is working exactly as designed, letting you know that unwanted moisture is present. Our job now is to figure out where that moisture came from.

Uncovering the Common Problems Causing Navien Error 353

While a “leak” sounds scary, the cause of the moisture isn’t always a dramatic pipe burst. In fact, the most common culprit is often far less severe. This section of our error 353 on navien tankless water heater guide breaks down the most frequent causes, from the simple to the more serious.

Condensation Buildup: The Most Likely Suspect

High-efficiency tankless water heaters like Navien units produce condensation as a normal part of their operation—much like your central air conditioner does in the summer. This condensation is supposed to be collected and drained away through a dedicated condensate line.

However, sometimes excess condensation can form and overwhelm the drain system, dripping down onto the leak sensor. This is especially common during:

Seasonal Changes: When the incoming ground water is very cold (like in the winter), the temperature difference inside the unit is greater, leading to more condensation.
Improper Venting: If the vent pipes aren’t sloped correctly, moisture that should be exiting outside can run back into the unit.
A Clogged Condensate Drain: Just like an AC drain line, this small tube can get clogged with sediment or debris, causing water to back up and spill inside the cabinet.

A Slow, Genuine Leak

Of course, sometimes the error is pointing to a true leak. This is less common than condensation but requires more immediate attention. The water could be coming from several places:

Loose Fittings or Connections: Over time, vibrations can cause water connections to loosen slightly, creating a slow drip.
Gasket or O-Ring Failure: The rubber seals within the unit can degrade over many years, eventually allowing water to seep out.
A Compromised Heat Exchanger: This is the most serious (and rarest) cause. A crack in the heat exchanger can cause a leak, often identified by rusty or discolored water.

External Water Intrusion

Sometimes the water isn’t coming from the Navien unit at all! It’s crucial to consider outside sources that could be dripping onto or into the water heater.

Look for things like a leaky plumbing pipe directly above the unit, a roof leak that has traveled down a wall, or even rain being driven into the exhaust vent during a severe storm. High humidity in the installation area (like a damp basement) can also contribute to moisture buildup.

A Faulty Leak Sensor

Last but not least, there’s a small chance the sensor itself has failed. It might be sending a “wet” signal to the control board even when it’s perfectly dry. This is typically diagnosed by a technician after all other potential sources of moisture have been ruled out.

Your Step-by-Step Guide to Safely Troubleshoot Error 353

Alright, it’s time to do some investigating. Before you even think about opening the unit’s cover, we need to talk about safety. This is non-negotiable.

!!! CRITICAL SAFETY WARNING !!!
Before performing any of the following steps, you MUST turn off the electrical power to your water heater at the circuit breaker. You should also shut off the gas supply valve (it usually has a red or yellow handle) and the main water inlet valve to the unit. Your safety is the number one priority.

Once you’ve confirmed the power, gas, and water are off, we can proceed with these simple checks.

Reset the System (The Easiest First Step): Sometimes, a power flicker or electronic glitch can trigger a false error. Go to your breaker panel and flip the breaker for your water heater off, wait a full minute, and then flip it back on. If the error clears and doesn’t return, you may have just had a temporary hiccup.
Perform a Thorough Visual Inspection (Exterior): Before opening anything, take a good look around the entire unit. Do you see any water stains on the wall behind it? Are there any drips coming from the pipes connected to the top or bottom? Check the floor directly underneath for any signs of moisture. This can help you spot an external leak source.
Carefully Remove the Front Cover: Most Navien units have a front cover held in place by a few screws at the bottom or sides. Remove them carefully and set the cover aside. This will give you a clear view of the internal components.
Locate the Leak Detection Sensor: Look at the very bottom of the unit’s internal cabinet. You should see a small, often white or black, sensor with a couple of wires coming from it. This is the component that triggered the alarm.
Inspect for Moisture: This is the moment of truth. Is there a visible pool of water at the bottom of the unit? Is the sensor itself wet to the touch? Or is the area just slightly damp, indicating condensation? Use a flashlight to get a good look at all the fittings and pipes directly above the sensor.
Dry the Area Completely: If you’ve found moisture, use a dry, soft cloth or paper towels to soak it all up. Be gentle around the sensor and wiring. For residual dampness, you can use a hairdryer on its lowest heat or cool air setting to gently dry the area. Never use high heat, as it can damage plastic components or wiring.
Reset and Test the Unit: Once you are 100% certain the area is dry, replace the front cover. Then, and only then, turn the water, gas, and electricity back on. Try to run a hot water tap. If the unit fires up and operates normally without the error returning, you may have solved the problem, especially if it was minor condensation.

When to Stop and Call a Navien-Certified Technician

Your safety and the health of your equipment are paramount. While the steps above can resolve simple issues, there are clear signs that it’s time to put the tools down and call a qualified professional. This is one of the most important error 353 on navien tankless water heater tips we can offer.

Call a pro immediately if you encounter any of these situations:

You find a steady, active drip or stream of water inside the unit.
The error code comes back right away after you’ve dried the sensor and reset the unit.
You see signs of rust, corrosion, or cracking on any major components, especially the heat exchanger.
The source of the water is not obvious, and you can’t trace it to a simple fitting.
You are not comfortable or confident performing any of the inspection steps outlined above.
Your Navien unit is still under warranty. Performing unauthorized work could void your coverage.

A certified technician has the diagnostic tools and experience to pinpoint the exact cause of the leak safely and efficiently, ensuring a proper, long-lasting repair.

Best Practices for Preventing Error 353 in the Future

Resolving the current error is great, but preventing it from happening again is even better. Adopting a few error 353 on navien tankless water heater best practices can improve your unit’s reliability and contribute to a more sustainable, eco-friendly operation by keeping it running at peak efficiency.

Schedule Annual Professional Maintenance

This is the single most effective thing you can do. During an annual tune-up, a technician will clean and inspect the entire system, including checking for minor leaks, cleaning the condensate drain, and ensuring all components are in good working order. This is the core of any good error 353 on navien tankless water heater care guide.

Keep the Condensate Drain Clear

Periodically check where your condensate line terminates to ensure it isn’t blocked by debris, algae, or ice in the winter. A clear drain path is essential for preventing water from backing up into the unit.

Monitor the Area Around Your Unit

Keep the space where your water heater is installed clean, dry, and free of clutter. Once a month, do a quick visual check of any plumbing or pipes located above the unit to catch potential external leaks early.

Frequently Asked Questions About Error 353 on Navien Tankless Water Heaters

Can I just bypass or disable the leak sensor to get my hot water back on?

Absolutely not. The leak sensor is a critical safety device. Bypassing it is like taking the batteries out of your smoke detector because it chirped. You would be ignoring a potential leak that could cause thousands of dollars in water damage to your home. Never disable a safety feature.

How much does it cost to fix Navien Error 353?

The cost can vary dramatically based on the cause. If it’s just condensation that you can dry yourself, the cost is $0. If a simple fitting needs to be tightened by a plumber, you might pay for a one-hour service call ($150-$300). If a major component like a heat exchanger has failed, the repair could be over $1,000. A professional diagnosis is the only way to know for sure.

Is Error 353 dangerous?

The error code itself is not dangerous—it’s a safety alert. The underlying cause, however, can be. An unchecked water leak can lead to significant property damage and create conditions for mold growth. The sensor is doing its job to alert you to the problem before it gets worse.

Tackling an error code on a sophisticated piece of equipment like a Navien tankless water heater can feel intimidating, but you’ve already taken the most important step: seeking out information. By following these safe, logical steps, you can diagnose and often resolve the most common cause of Error 353.

Remember to always prioritize safety. Work methodically, and don’t hesitate to call a trusted professional when you’re out of your comfort zone. You’ve got this!

Here’s to getting that hot water flowing reliably again. Stay safe and stay comfortable!

Author
Recent Posts

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.