Why Is My Navien Water Heater Leaking - A Pro'S Step-By-Step

That sinking feeling in your stomach when you spot a puddle of water under your Navien tankless water heater is something no homeowner wants to experience. Your mind immediately races: Is this a simple drip or a catastrophic failure? How much is this going to cost? Don’t panic. We’ve been there, and we’re here to help.

As HVACR technicians, we know that a leak can seem intimidating, but often, the cause is something you can identify—and sometimes even fix—safely. We promise to walk you through the entire process, just like we would with a client in their home. This is your complete why is my navien water heater leaking guide, designed to help you pinpoint the source of the leak and understand your next steps.

In this article, you’ll learn how to safely assess the situation, identify the most common leak points from simple connections to more complex internal parts, and understand the crucial difference between a quick DIY fix and a “call a pro now” situation. Let’s get that leak under control.

First Steps: How to Safely Assess the Leak

Before you start poking around, safety is your number one priority. Navien units involve water, electricity, and gas—a combination that demands respect. Taking a few moments to secure the area will protect you and your home from further damage.

Step 1: Shut Off Power and Water

Your first move should always be to isolate the unit. This prevents electrical hazards and stops more water from feeding the leak.

Kill the Power: Find the circuit breaker dedicated to your water heater in your home’s electrical panel and switch it to the “OFF” position. Some units may also have a power switch on or near the unit itself.
Turn Off the Water: Locate the cold water inlet valve leading into your Navien. It usually has a blue handle. Turn it clockwise until it stops. This will cut off the water supply to the heater.
Turn Off the Gas (If Applicable): Find the gas shutoff valve on the gas line connected to your unit. It typically has a yellow or red handle. A quarter turn, so the handle is perpendicular to the pipe, will shut off the gas.

Step 2: Identify the Source of the Water

Now that the area is safe, it’s time to play detective. Is the water coming from a specific pipe, a valve, or the main body of the unit itself? Dry the unit and the surrounding area thoroughly with a towel. This will help you see exactly where new water is originating.

Observe the leak. Is it a slow, steady drip? A more aggressive stream? Or is it just condensation? Knowing the nature of the leak provides valuable clues.

Common Problems with Why Is My Navien Water Heater Leaking

With Navien tankless units, leaks often originate from a few usual suspects. Let’s work our way from the most common (and often easiest to fix) issues to the more complex ones. These checks are the foundation of any good troubleshooting process.

The Pressure Relief Valve (PRV)

The most common source of a leak on any water heater is the Temperature and Pressure Relief Valve, or PRV. This is a critical safety device designed to release water if the pressure or temperature inside the unit gets too high.

Why it leaks:

High Water Pressure: If your home’s water pressure is over 80 PSI, it can force the valve open.
Debris: A tiny piece of sediment or mineral scale can get stuck in the valve seat, preventing it from closing completely.
Valve Failure: Like any mechanical part, the PRV can simply wear out and fail over time.

What to do: Check if water is dripping from the PRV’s downward-facing discharge pipe. If it is, the issue could be high pressure (a system-wide problem) or a faulty valve (a component problem).

Loose Plumbing Connections

Your Navien unit is connected to your home’s plumbing with several fittings for hot water out, cold water in, and gas. Over time, the vibrations from the unit’s operation can cause these connections to loosen slightly.

Carefully inspect the threaded fittings where the flexible water lines connect to the unit’s service valves. You might see a slow drip forming right at the nut. Sometimes, a gentle tightening with a wrench (don’t over-tighten!) is all that’s needed to solve the problem.

The Condensate Line

As a high-efficiency condensing unit, your Navien produces acidic water (condensate) as a byproduct of combustion. This water is drained away through a plastic tube, usually PVC.

If this condensate drain line becomes clogged with debris or freezes, the water will back up and overflow from the unit’s internal collection pan. This can easily be mistaken for a leak. Check that the drain line is clear and has a proper downward slope.

Decoding More Serious Issues: When the Leak is Internal

If you’ve checked all the external connections and valves and still can’t find the source, the problem is likely inside the unit’s casing. These issues almost always require a certified technician, but understanding them can help you communicate the problem effectively.

A Cracked or Failed Heat Exchanger

The heat exchanger is the heart of your Navien unit. A crack in this component is a serious failure. This is often caused by excessive mineral scale buildup from hard water, which creates hot spots that stress the metal, or from freeze damage.

A leak from a heat exchanger will typically appear as water dripping from the very bottom of the unit’s casing. Unfortunately, this is often a fatal flaw, and replacing the heat exchanger can be as expensive as a new unit.

Internal O-Rings, Gaskets, or Hoses

Inside the compact casing of your Navien are numerous small hoses, O-rings, and gaskets that seal various components. Over years of heating cycles and exposure to water, these rubber and plastic parts can become brittle, crack, and fail.

A leak from one of these small components can be difficult to pinpoint without disassembling the unit—a job best left to a professional who knows the system inside and out.

Your Navien Water Heater Care Guide: Best Practices for Prevention

The best way to deal with a leak is to prevent it from ever happening. Following a few why is my navien water heater leaking best practices can dramatically extend the life of your unit and save you from costly repairs. This is the key to a sustainable and eco-friendly approach to hot water.

Embrace Annual Flushing and Descaling

This is the single most important maintenance task for any tankless water heater. Minerals like calcium and magnesium in your water build up inside the heat exchanger over time, forming a hard layer called “scale.”

This scale insulates the heat exchanger, forcing the unit to work harder and creating damaging hot spots that can lead to cracks and leaks. Flushing your unit annually with a descaling solution dissolves this buildup, protecting the core of your heater.

Consider a Water Softener

If you live in an area with very hard water, the most sustainable solution is to install a whole-home water softener. This system removes the minerals before they ever enter your Navien, preventing scale buildup not just in your water heater, but in all your pipes and appliances.

When to DIY vs. When to Call a Certified Navien Technician

Knowing your limits is key to a successful and safe outcome. Here’s a clear breakdown of what you can tackle and when to pick up the phone.

Safe DIY Checks You Can Perform

Verifying that water and power are shut off.
Visually inspecting external connections for drips.
Gently tightening a loose water connection (e.g., a quarter turn past “snug”).
Checking the condensate drain line for obvious clogs or blockages.

Red Flags: Call a Professional Immediately If…

The leak is coming from inside the main white casing of the unit.
You see any error codes on the digital display.
You suspect the leak is from the Pressure Relief Valve (this could indicate a dangerous pressure issue).
You smell gas or are not 100% confident in performing any of the steps.
The leak is significant and causing water damage.

A certified Navien technician has the diagnostic tools, replacement parts, and specific training to safely open the unit, pinpoint the internal failure, and perform the repair correctly.

Frequently Asked Questions About Leaking Navien Water Heaters

Is a small, slow drip from my Navien a big deal?

Yes. Any unmanaged water leak is a problem. What starts as a small drip can quickly worsen, leading to significant water damage, mold growth, and potential damage to the unit’s internal electronics. Address it immediately.

How much does it cost to fix a leaking Navien water heater?

The cost varies dramatically depending on the cause. A loose connection might cost you nothing but a few minutes of your time. A failed PRV could be a couple of hundred dollars for parts and labor. A cracked heat exchanger, however, could cost thousands and may warrant a full unit replacement.

Can I still use my Navien if it has a tiny leak?

We strongly advise against it. You don’t know the cause of the leak, and continuing to operate the unit could worsen the damage or create a safety hazard, especially if water gets into the electronic components.

Finding a leak is stressful, but you’ve already taken the most important step by seeking out information. By following this guide, you can safely assess the situation, identify common issues, and make an informed decision about your next steps. Proper maintenance is your best defense, ensuring you get years of reliable, efficient hot water from your Navien unit.

Stay safe, stay informed, and don’t hesitate to call a trusted professional when you’re out of your comfort zone!

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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.