How To Clean A Navien Tankless Hot Water Heater - A Step-By-Step Guide

Is your once-reliable Navien tankless water heater acting up? Maybe you’re noticing lukewarm showers, fluctuating water pressure, or strange rumbling sounds. It’s a common frustration, and that feeling of dread about a potential repair bill is something every homeowner can agree on.

I promise you, there’s a very good chance the solution is simpler and cheaper than you think. In my years as an HVACR technician, I’ve seen countless “broken” units brought back to life with one simple procedure.

This comprehensive guide will walk you through exactly how to clean a Navien tankless hot water heater, just like a pro. We’ll cover why it’s essential, what tools you’ll need, the safe, step-by-step flushing process, and pro tips to keep your unit running at peak efficiency for years to come. Let’s get that hot water flowing reliably again!

Why Cleaning Your Navien Tankless Heater is Non-Negotiable

Think of your tankless water heater like the arteries in your body. Over time, minerals in your water—primarily calcium and magnesium—build up inside the tiny, intricate pathways of the heat exchanger. This buildup is called “scale,” and it’s the number one enemy of your Navien.

Ignoring this scale buildup leads to a cascade of issues. Understanding the benefits of how to clean a navien tankless hot water heater is the first step toward protecting your investment.

The Problem with Mineral Scale

Reduced Efficiency: Scale acts as an insulator, forcing your heater to work much harder and burn more fuel to heat the water. This means higher energy bills for less performance.
Decreased Water Flow: As the pathways clog with scale, the volume of water that can pass through is restricted, leading to frustratingly low water pressure at your taps and showerheads.
Component Failure: The extra strain on the heat exchanger can cause it to overheat and fail prematurely. This is often the most expensive component to replace—sometimes costing nearly as much as a new unit.
Shorter Lifespan: A well-maintained Navien can last 20 years or more. A neglected one might fail in less than half that time. Regular cleaning is the best life insurance for your heater.

A routine cleaning, or “descaling,” dissolves this mineral buildup, restoring your unit to factory-fresh performance. It’s the single most important piece of maintenance you can perform.

Gathering Your Tools & Materials: The DIY Descaling Kit

Before we dive in, let’s get our toolkit ready. Don’t worry, you don’t need a truck full of specialized equipment. Most of these items are readily available at any hardware store, or you can buy a pre-packaged descaling kit online.

Here’s what you’ll need for this how to clean a navien tankless hot water heater guide:

A 3-5 Gallon Bucket: This will hold your cleaning solution.
A Small Submersible Pump: A simple utility pump with at least 350 GPH (gallons per hour) flow is perfect.
Two Washing Machine Hoses: Standard 3-4 foot hoses with female connectors on both ends are ideal. Make sure they are in good condition with no cracks.
Descaling Solution: You have two main options here.
- Food-Grade White Vinegar: A safe, affordable, and eco-friendly how to clean a navien tankless hot water heater option. You’ll need about 2-4 gallons.
- Commercial Descaler: A concentrated solution specifically designed for potable water heaters. It works faster but be sure to choose one that is non-toxic and NSF-certified.
Channel Locks or an Adjustable Wrench: For loosening and tightening hose connections.
Towels: For catching any minor drips and spills.

Pro Tip: Many homeowners find it convenient to purchase a “tankless water heater flush kit.” These kits bundle the pump, hoses, and sometimes the descaler into one package, taking the guesswork out of it.

The Step-by-Step Guide on How to Clean a Navien Tankless Hot Water Heater

Alright, you’ve got your tools and you understand the “why.” Now for the “how.” Follow these steps carefully, and you’ll have this done in about an hour. Don’t rush—safety and thoroughness are key.

Step 1: Safety First – Power Down the Unit

Before you touch anything, you must cut power to the water heater. Unplug the unit from the wall outlet. If it’s hardwired, shut off the corresponding breaker in your electrical panel. This is a critical safety step you cannot skip.

Step 2: Shut Off the Water and Isolate the Heater

Your Navien unit has three water valves located underneath it: a blue handle for the cold water inlet, a red handle for the hot water outlet, and a yellow handle for the gas line. Leave the gas line ON.

Turn the blue and red handles perpendicular to the pipe to shut off the water supply to and from the heater.
Your unit has service ports on these valves. You’ll see small T-shaped handles on them. Slowly turn these handles to open the service ports. This isolates the heater from your home’s plumbing and allows you to connect your hoses. A little water may drip out, which is normal.

Step 3: Connect Your Hoses and Pump

It’s time to create our cleaning loop. This setup will circulate the descaling solution through the heater.

Connect one hose to the cold water service port (the blue one). Place the other end of this hose into your empty bucket.
Connect the second hose to the hot water service port (the red one). Attach the other end of this hose to the outlet of your submersible pump.
Place the submersible pump at the bottom of your bucket.

Step 4: Add and Circulate the Descaling Solution

Pour your descaling solution into the bucket. If using vinegar, pour in about 2-3 gallons. If using a commercial descaler, follow the manufacturer’s instructions for dilution—you’ll likely mix it with water.

Ensure the solution in the bucket is high enough to fully submerge the pump. Plug in the pump. You should hear it whir to life and see the solution being pushed from the bucket, through the hot water port, into the Navien, and back out the cold water port into the bucket.

Let this circulate for at least 45 to 60 minutes. You might see the solution get cloudy or change color as it dissolves the mineral scale. That’s a good sign—it means it’s working!

Step 5: Flush the System with Fresh Water

After circulating, it’s time to flush out the loosened debris and cleaning solution.

Unplug the pump.
Remove the hose from the pump and leave it in the bucket.
Keeping the hot water hose in the bucket, close the hot water service port (the red one).
Slowly open the main cold water valve (the blue handle). This will push fresh water through the heater, flushing the remaining solution and debris out of the hot water hose and into the bucket.
Let it flush for about 5 minutes, or until the water runs clear and you no longer smell vinegar or the descaler.

Step 6: Clean the Inlet Water Filter

This is one of the most important how to clean a navien tankless hot water heater tips that people often forget! Your Navien has a small screen filter on the cold water inlet to catch larger debris.

Unscrew the cold water line connection at the bottom of the unit. You’ll see a small filter screen inside. Carefully pull it out with needle-nose pliers and rinse it under a faucet until it’s clean. Then, re-insert it and reconnect the water line.

Step 7: Restore Normal Operation

You’re in the home stretch! Let’s get everything back to normal.

Turn off the main cold water valve again.
Remove your hoses from the service ports.
Close both the hot and cold service ports by turning the small T-handles back to their original positions.
Slowly open the main hot and cold water valves (red and blue handles).
Go to the nearest hot water faucet in your home and turn it on. It will sputter as air escapes the lines. Let it run until you have a smooth, steady stream.
Check all your connections under the Navien for any leaks.
Once you’re sure there are no leaks, plug the unit back in or flip the breaker back on. Your Navien will power up and be ready for service.

Common Problems and Best Practices

Even with a perfect guide, things can sometimes go sideways. Here are some solutions to common problems with how to clean a navien tankless hot water heater and some best practices to ensure a smooth process.

Troubleshooting Common Issues

Pump Won’t Start: Make sure it’s fully submerged and plugged into a working outlet. Some pumps have an airlock; tilting it underwater can help release trapped air.
Low Flow During Flush: Your inlet filter might be severely clogged. Double-check it. It could also mean you have a very heavy scale buildup that is restricting flow.
Error Code After Cleaning: The most common is a flow sensor error. This is often caused by debris getting stuck in the sensor during flushing. You can sometimes clear it by running a hot water tap on full blast for a few minutes. If it persists, you may need a technician to clean the sensor itself.

Following these how to clean a navien tankless hot water heater best practices will help you avoid these issues and ensure a long, efficient life for your unit.

How Often Should You Clean Your Navien? A Simple Care Guide

The ideal cleaning frequency depends entirely on your local water hardness. Harder water means more minerals and a greater need for descaling. This how to clean a navien tankless hot water heater care guide provides a general schedule:

Soft Water: Every 2-3 years.
Moderately Hard Water: Annually (this applies to most households).
Very Hard Water or Well Water: Every 6-9 months.

If you’re unsure about your water hardness, you can buy a simple test kit or check your municipal water report online. Investing in a whole-home water softener is the ultimate sustainable how to clean a navien tankless hot water heater solution, drastically reducing the need for frequent descaling.

Frequently Asked Questions About Cleaning a Navien Tankless Heater

Can I use CLR or another harsh chemical to clean my Navien?

Absolutely not. Harsh chemicals like CLR can be too aggressive and damage the delicate rubber gaskets, O-rings, and even the metal components inside your heater. Stick with food-grade white vinegar or a descaler specifically formulated for potable tankless water heaters.

What happens if I never descale my tankless water heater?

Neglecting this maintenance will lead to a slow and expensive death for your unit. You’ll experience decreased performance, higher energy bills, fluctuating temperatures, and eventually, a catastrophic failure of the heat exchanger, which is the most costly part to replace.

How do I know if my Navien needs cleaning?

Your unit will give you signs! The most common indicators are a noticeable drop in water pressure when using hot water, water that doesn’t get as hot as it used to, or the unit displaying an error code related to flow or overheating. Don’t wait for these signs—be proactive with an annual cleaning.

Congratulations! You now have the knowledge and confidence to perform this essential maintenance yourself. By taking an hour each year to complete this process, you’re not just ensuring endless hot showers; you’re protecting your investment, saving money on energy bills, and preventing a premature and costly replacement.

Stay safe, and enjoy that perfectly performing Navien!

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.