Navien Tankless Water Heater Error Code 762 - Your Step-By-Step

That sinking feeling when you step into a cold shower is bad enough. But seeing a blinking “navien tankless water heater error code 762” on your unit’s display can turn a minor annoyance into a major source of stress. What does it mean? Is it a serious problem? Can you fix it yourself?

We understand your frustration, and we’re here to help. At HVACRLY, we believe that with the right guidance, you can confidently tackle many common HVACR issues.

We promise this guide will demystify Error Code 762 and provide you with a clear, safe, and logical path to getting your hot water flowing again. We’ll walk you through what this specific code means, the most common culprits behind it, and a step-by-step troubleshooting process. You’ll learn what you can safely check yourself and, just as importantly, when it’s time to call in a professional.

Let’s get that hot water back on track.

What Exactly is Navien Error Code 762? A Simple Explanation

First things first, let’s take the mystery out of the number. In the world of Navien tankless water heaters, Error Code 762 points directly to a “Water Flow Sensor Malfunction.”

Think of the water flow sensor as the gatekeeper for your heater. Its only job is to detect when you turn on a hot water tap somewhere in your house. When it senses water moving through the pipes, it sends a signal to the main control board that says, “Hey, it’s time to fire up the burner and make some hot water!”

If this sensor fails, is blocked, or can’t send a clear signal, the control board gets confused. To protect itself and prevent damage, the unit shuts down and displays Error Code 762. Essentially, your heater is telling you, “I don’t think water is flowing, so I’m not going to turn on.”

Uncovering the Common Problems with Navien Tankless Water Heater Error Code 762

While the error code points to the flow sensor, the sensor itself isn’t always the villain. Several issues can trick the sensor or prevent it from working correctly. As technicians, we usually see this error stemming from a few key areas. This is our initial checklist.

Here are the most common problems that trigger this fault:

A Clogged Inlet Water Filter: This is, by far, the most frequent cause. Your Navien has a small screen filter on the cold water inlet pipe to catch sediment and debris. Over time, this filter can get clogged, severely restricting water flow. If not enough water can get into the heater, the flow sensor won’t activate properly.
Low Household Water Pressure: Tankless water heaters require a minimum amount of water pressure and flow to operate. If your home’s overall water pressure is too low, or if multiple fixtures are running at once, there might not be enough force to trigger the flow sensor.
A Faulty Flow Sensor: Like any electronic component, the flow sensor can simply wear out and fail over time. It might get stuck, or its internal components could break down, preventing it from sending the correct signal.
Wiring or Connection Issues: The flow sensor is connected to the main control board by a set of wires. A loose connection, a corroded pin, or a damaged wire can interrupt the signal, leading the control board to believe the sensor has malfunctioned.
Debris Inside the Sensor Assembly: Sometimes, a small piece of sediment or scale can get past the main filter and become lodged inside the flow sensor’s assembly, physically preventing it from moving and detecting flow.

Your Step-by-Step Navien Tankless Water Heater Error Code 762 Guide

Alright, let’s roll up our sleeves. We’re going to walk through a few safe checks together, starting with the easiest and most common fixes. Follow these steps in order. Before you begin any of these checks, press the power button on the front panel to turn the unit off. For added safety, you can also unplug it or turn off the breaker that powers it.

Step 1: The Easiest First Check – Reset Your Unit

Before we take anything apart, let’s try the simplest solution. Sometimes, a temporary glitch can cause an error code. A simple power cycle can clear the unit’s memory and resolve the issue.

Press the power button on the front of your Navien unit to turn it off.
Wait for a full 60 seconds. This allows the internal capacitors to discharge completely.
Press the power button again to turn it back on.
Go to a nearby sink and turn on the hot water tap fully. Listen to see if the water heater fires up.

If the error code disappears and you get hot water, you may have just experienced a momentary glitch. If the navien tankless water heater error code 762 comes right back, it’s time to move on to the next step.

Step 2: Inspect and Clean the Inlet Water Filter

This is the big one. A clogged filter is the culprit in more than 70% of Error 762 cases we see in the field. This is a crucial part of any navien tankless water heater error code 762 care guide.

You will need: A bucket, an adjustable wrench or channel-lock pliers, and an old toothbrush.

Locate the Cold Water Inlet: Look at the pipes connected to the bottom of your Navien unit. You should see three pipes. They are typically labeled or color-coded: red for hot out, blue for cold in, and a larger one for gas. We are focused on the blue cold water inlet pipe.
Turn Off the Water: Find the service valve on the cold water pipe (it will have a blue handle). Turn the handle 90 degrees so it is perpendicular to the pipe. This shuts off the water supply to the heater. Do the same for the hot water valve (red handle).
Relieve the Pressure: Open the small pressure relief valve on the cold water service valve to drain the remaining water from the line. Place your bucket underneath to catch the water.
Remove the Filter Plug: Just behind the cold water service valve, you’ll see a large plug or cap. Use your wrench or pliers to carefully unscrew it (counter-clockwise). A little more water will come out, which is normal.
Clean the Filter: Inside, you’ll find a small, cylindrical mesh screen. Gently pull it out. Take it to a sink and rinse it under running water. Use an old toothbrush to gently scrub away any stubborn sediment or scale buildup. Hold it up to the light to ensure it’s completely clean.
Reassemble: Carefully place the clean filter back into its housing, ensuring it’s seated correctly. Screw the plug back in, hand-tightening it first and then giving it a gentle quarter-turn with your wrench to ensure a good seal. Do not overtighten.
Restore Water and Power: Slowly turn the cold and hot water service valves back on. Check for any leaks around the plug you just tightened. If all is dry, restore power to the unit and try running the hot water again.

For many of you, this will solve the problem. If the error persists, let’s check the next possibility.

Step 3: Evaluate Your Home’s Water Pressure

Tankless heaters are sensitive to flow. If the pressure is too low, the unit won’t operate. You can get a simple screw-on pressure gauge from any hardware store for about $10.

Attach it to an outdoor hose bibb or your washing machine’s cold water hookup. A healthy residential water pressure is typically between 40 and 80 PSI. If your pressure is below 40 PSI, it could be the source of your problem. This could be due to a partially closed main water valve for your house or an issue with your municipal supply or well pump.

When to Stop and Call a Certified Navien Technician

We’ve now reached the limit of what we recommend for most homeowners. If you’ve reset the unit, thoroughly cleaned the filter, and confirmed you have adequate water pressure, but the navien tankless water heater error code 762 remains, the problem lies deeper within the unit.

The next steps involve checking voltage at the flow sensor, inspecting internal wiring harnesses, and potentially replacing the sensor itself. These tasks require specialized tools (like a multimeter) and a deep understanding of the unit’s electronics and safety protocols.

Call a licensed and certified Navien technician if:

The error code persists after cleaning the filter and checking pressure.
You are not 100% comfortable working with plumbing connections.
You suspect the issue is with the sensor itself or the internal wiring.
The unit is making any unusual noises or showing other error codes.

Working inside the unit without proper training can lead to further damage, void your warranty, or create a safety hazard. A professional can diagnose the issue quickly and safely, ensuring the repair is done right.

Preventative Maintenance: Best Practices to Avoid Future Errors

An ounce of prevention is worth a pound of cure—and a cold shower. Following a few navien tankless water heater error code 762 best practices can keep your unit running smoothly for years.

Clean the Inlet Filter Regularly: Mark your calendar to check and clean that little filter every 6 months. If you have hard water or well water, you may need to do it every 3 months.

Annual System Flush (Descaling): Hard water minerals (calcium and magnesium) are the mortal enemy of tankless heaters. These minerals build up inside the heat exchanger, restricting flow and reducing efficiency. Performing an annual flush with a descaling solution keeps the internal pathways clear. This is a key part of creating a sustainable navien tankless water heater error code 762 prevention plan.

Professional Tune-Up: Have a qualified technician inspect your unit once a year. They can check gas pressure, inspect the burner and igniter, and catch small issues before they become big, expensive problems.

The Eco-Friendly Advantage of a Well-Maintained Navien Heater

Following a proper care guide isn’t just about avoiding errors; it’s about efficiency. A clean, well-maintained Navien unit operates at its peak performance. When scale builds up or filters are clogged, your heater has to work harder and burn more gas to produce the same amount of hot water.

By keeping your system clean, you’re not only preventing frustrating error codes but also ensuring you’re getting the energy savings you invested in. A properly functioning unit is an eco-friendly navien tankless water heater error code 762 solution—it uses less energy, lowers your utility bills, and extends the lifespan of the appliance, reducing waste.

Frequently Asked Questions About Navien Error Code 762

Can I still use my water heater if it shows Error Code 762?

No. Error Code 762 is a “hard lockout,” meaning the unit will not attempt to heat water until the underlying issue is resolved. This is a safety feature to prevent the burner from firing without adequate water flow, which could damage the heat exchanger.

How much does it cost to fix Navien Error Code 762?

The cost can vary dramatically. If the issue is simply a clogged filter that you clean yourself, the cost is $0. If you need a technician to come out and clean it, you might pay a service call fee (typically $75-$150). If the flow sensor itself needs to be replaced, the part can cost between $50-$100, plus labor, bringing the total repair cost to roughly $200-$400.

How often should I flush my Navien tankless water heater?

This depends on your water hardness. For areas with moderately hard water, once a year is recommended. If you have very hard water, you may need to do it every 6-9 months. You can check your local municipality’s water quality report online to find out your water hardness level.

Dealing with a water heater error is never fun, but hopefully, this guide has empowered you to understand the problem and take the right steps. By tackling the simple checks first, you can often solve the issue yourself and get back to enjoying that endless hot water. For everything else, your local HVACR pro is just a call away.

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.