Navien Water Heater Code 736-00 - Your Step-By-Step Troubleshooting

That sudden drop in your stomach when your state-of-the-art Navien tankless water heater stops working and flashes an error code is a feeling no homeowner enjoys. If you’re currently looking at Navien water heater code 736-00 on your unit’s display, you’re likely concerned about a potential leak and the looming threat of cold showers.

But take a deep breath—you’ve come to the right place. While any error code can be intimidating, this one is often solvable. We promise to guide you through exactly what this code means, what safe steps you can take to diagnose the issue yourself, and when it’s the right time to call in a professional.

In this comprehensive guide, we’ll break down the causes, provide a clear troubleshooting checklist, and share some pro tips to get your hot water flowing again. Let’s get that Navien back in top shape.

What Exactly is Navien Water Heater Code 736-00?

First things first, let’s decode the message your water heater is sending you. The Navien water heater code 736-00 is a “System Leak Detected” error. It’s a smart safety feature built into models equipped with the NaviCirc™ recirculation system.

Think of it like a tiny, vigilant guard inside your water heater. This system constantly monitors the water pressure within the domestic hot water (DHW) recirculation line. If it detects a steady drop in pressure when no hot water is being used, it assumes there’s a leak somewhere in the system.

To protect your home from potential water damage and prevent the unit from running dry, it proactively shuts down and displays the 736-00 code. So, while it’s an inconvenience, it’s also your water heater looking out for you.

Before You Begin: A Quick Safety Check

Before you touch anything, safety is our number one priority. We’re going to walk through a few simple checks, but let’s set the ground rules to ensure you and your home stay safe.

Power Down: If you see any visible water pooling around the unit, immediately shut off the electrical power to the water heater at your circuit breaker. Water and electricity are a dangerous mix.
Shut Off the Water: Locate the main water shut-off valve for the heater or your entire home and turn it off if you have an active, visible leak.
Gather Your Tools: For these initial checks, you won’t need much. Grab a powerful flashlight and some dry paper towels. That’s it!

Remember, the goal here is to diagnose, not to perform complex repairs. We’ll make it very clear when it’s time to hand the wrench over to a licensed technician.

Your Step-by-Step Guide to Troubleshooting Code 736-00

Alright, let’s roll up our sleeves and investigate. Follow these steps in order to methodically track down the source of the pressure drop. This is the core of our navien water heater code 736-00 guide.

Step 1: The Visual Inspection — Hunt for Obvious Leaks

The most common cause of a leak code is, well, a leak! But it might not be a gushing pipe. Often, it’s a very slow, sneaky drip that’s hard to spot.

Check Around the Unit: Using your flashlight, carefully inspect the floor and walls around your Navien water heater. Look for any signs of moisture, water stains, or mineral buildup (a white or greenish crust).
Inspect the Connections: Trace the water lines connected to the bottom of your unit. Pay close attention to the hot, cold, and recirculation line fittings.
The Paper Towel Test: This is a great pro tip. Take a dry paper towel and dab each pipe fitting and connection point. Even a tiny, imperceptible leak will leave a damp spot on the paper.

If you find a leak directly on or around the unit, the problem is found. At this point, it’s best to keep the water off and call a plumber.

Step 2: Check Your Home’s Water Fixtures

Here’s something many people miss: the “leak” might not be from a pipe at all! A constantly running toilet or a dripping hot water faucet can create a slow, steady pressure drop that tricks the Navien sensor.

Listen for Toilets: Walk through your home and listen for any toilets that might be running or refilling intermittently. This is a very common “phantom leak.”
Check All Hot Water Taps: Systematically check every faucet, showerhead, and tub spout in your house. Look for even the slightest drip… drip… drip… from the hot water side.
Don’t Forget Appliances: Check the hot water hose connection to your washing machine to ensure it’s tight and dry.

If you find a dripping faucet, tighten it or replace the washer. This simple fix could be all you need to resolve the 736-00 code.

Step 3: Inspect the Pressure Relief Valve (PRV)

The Temperature and Pressure Relief (TPR or PRV) valve is a critical safety device on your water heater. It’s designed to open and release water if the pressure or temperature gets too high. Sometimes, these valves can fail and develop a slow weep.

Locate the valve (it will have a small lever on top and a pipe leading down towards the floor). Check the end of the discharge pipe for any drips or signs of moisture. A faulty PRV is a common problem and requires professional replacement.

Step 4: Resetting the System (The Right Way)

If you have completed the inspections above and found no visible leaks or dripping faucets, you can attempt to reset the unit. Do not do this if you found a leak.

Simply press the power button or reset button on the front panel of your Navien unit. The system will restart. Monitor it closely. If the 736-00 code reappears quickly, it confirms there is a persistent issue that needs to be addressed.

Common Problems with Navien Water Heater Code 736-00

Understanding the “why” behind the code can help you pinpoint the issue faster. Here are the most frequent culprits our technicians encounter in the field.

The Hidden Leak: Weeping Fittings and Pinholes

The most straightforward cause is a tiny, physical leak. This could be from a poorly soldered pipe fitting, a degraded seal, or a pinhole leak in the recirculation line itself. These are often the hardest for homeowners to find, as they can be very small and hidden from view.

Air in the Recirculation Line

If you’ve recently had plumbing work done or the water to your home was shut off, air can get trapped in the recirculation line. This trapped air can compress and expand, causing pressure fluctuations that the sensor interprets as a leak. Purging the air from the line is a solution, but it’s a task best left to a technician to ensure it’s done correctly.

A Failing Component

Sometimes, the problem lies within the unit itself. The internal recirculation pump could have a failing seal, or the pressure sensor itself could be malfunctioning and giving a false reading. Diagnosing a faulty component requires specialized tools and knowledge of the unit’s internal workings.

When to Put Down the Tools and Call a Navien Pro

A DIY spirit is fantastic, but knowing your limits is crucial for safety and preventing more expensive damage. Here is your clear-cut checklist for when to call a licensed and certified technician.

You find any visible leak on or directly around the water heater unit.
The error code returns immediately after you reset it.
You are uncomfortable or unsure about performing any of the checks listed above.
You suspect the issue is internal to the unit, like the pump or a sensor.
Your Navien water heater is still under warranty (a DIY repair could void it).

A professional has the diagnostic tools to accurately test system pressure and pinpoint the exact location of a leak, saving you time, frustration, and potential water damage.

Navien Water Heater Code 736-00 Best Practices

Preventing future issues is the best strategy. Think of this error code not as a failure, but as a helpful alert. Adopting a good navien water heater code 736-00 care guide can improve reliability.

One of the key benefits of navien water heater code 736-00 is that it alerts you to water-wasting leaks early. Fixing them is not only good for your unit but also serves an eco-friendly navien water heater code 736-00 goal by conserving water and the energy used to heat it.

Regular annual maintenance, including checking connections and descaling the unit (especially in hard water areas), is the single best thing you can do to extend its life and prevent unexpected shutdowns.

Frequently Asked Questions About Navien Water Heater Code 736-00

Can I just keep resetting the error code if it keeps appearing?

We strongly advise against this. The error code is a safety alert. Repeatedly ignoring it means you are ignoring an underlying problem, likely a leak. This can lead to significant water damage to your home, mold growth, and eventually a complete failure of the unit.

How much does it cost to fix a 736-00 error?

The cost can vary dramatically. If the cause is a simple dripping faucet that you fix yourself, the cost is virtually $0. If it’s a loose fitting that a plumber tightens, it might just be the cost of a service call. However, if an internal component like the recirculation pump needs to be replaced, the cost could be several hundred dollars for parts and labor.

Is the 736-00 error code dangerous?

The code itself is not dangerous; it’s a safety feature. The potential underlying cause—a water leak—is what you need to take seriously. While it’s not an immediate emergency like a gas leak, an unaddressed water leak can cause severe structural damage, ruin flooring and drywall, and lead to costly repairs over time.

Facing an error code on your Navien water heater can be stressful, but by following this guide, you are now equipped with the knowledge to safely investigate the 736-00 code. Remember to work through the steps methodically: inspect for obvious leaks, check your home’s fixtures, and never hesitate to call a trusted professional when you’re out of your depth.

You’ve taken the first and most important step by seeking out information. Now you can confidently tackle the problem. 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.