How To Flush Navien Tankless Water Heater [Fully Explained]

If you know anything about tankless water heaters, you know that flushing them is paramount if you want them to last long. But you may be confused if you can do this job on your own or if you need professional help. So, how to flush Navien tankless water heater?

From my own experience of working on numerous Navien heaters, I can tell you that flushing Navein water is an easy job. Anybody can do it as long as the tools are available. I’ve broken down the flushing procedure into simple steps in this guide.

Moreover, you’ll know about how often you should flush your water heater along with other helpful maintenance tips. So, let’s dive in!

how to flush navien tankless water heater

Why Should You Flush Navien Tankless Water Heater?

Before I dive deeply into the Navien flushing instructions, you should know why flushing your water heater is important. A tankless water heater offers a great advantage over the traditional water heater as it eliminates the need for a large storage tank.

But you need to maintain the tankless water heater properly. Otherwise, you’d see a reduction in the efficiency and performance of your water heater. Flushing the heat exchanger is the most important task on your tankless water heater. Let’s take a detailed look at why it’s so crucial.

01. Removing Sediments From The Heat Exchanger

It’s highly likely that the water you’re using isn’t 100% clean. No matter how good the quality of the water in your area is, it’ll have some impurities. If the water supply in your area is not good, it’ll have even more dirt.

Such dirt and sediments will settle on the heat exchanger and end up clogging it. So, the performance of the water heater will reduced and the heat exchanger will also get damaged with time. You need to flush the water heater to remove the sediments and protect your heat exchanger.

02. Keeping The Minerals From Building Up

Just like dirt, minerals like Calcium and Magnesium will settle in the heat exchanger of your Navien water heater with time. This scale formation is often paralyzing to the water heater as it reduces the water flow of the heater.

The good news is that flushing the water heater will descale the heat exchanger and get rid of the minerals inside it. So, the water heater will have optimal water flow and you won’t have to worry about any performance issues.

03. Maintaining The Energy Efficiency Of Your Water Heater

One of the main advantages of a tankless water heater is that they’re highly energy efficient compared to tank-style water heaters. That’s primarily because of the heat exchanger. It heats the water as soon as there’s any demand for hot water and a hot water faucet is opened.

But the heat exchanger will only do that when it’s in good condition. If you don’t flush your heater, the sediments, dirt, and minerals inside it will compromise its energy efficiency. So, you must flush your water heater to keep it energy-efficient and reduce your utility bills.

04. Improving The Quality Of The Water You Use

If there are minerals and dirt piled up on the heat exchanger, you’ll also find them in the hot water you use. Not all the dirt will stay on the heat exchanger. Some of them will come out through the hot water faucet.

So, the quality of the hot water you’ll use will be very poor. The water can even have a bad smell and taste in severe cases. Flushing the water heater will get rid of those things and ensure that the water you’re using is good.

05. Extend The Lifespan Of Your Water Heater

If you go a long time without flushing the water heater, the heat exchanger will become corroded. Eventually, it’ll become cracked and get completely damaged. The heat exchanger is the heart and soul of a tankless water heater.

If the heat exchanger gets damaged after the warranty has expired, you’d have to replace the water heater. But you can avoid that issue by flushing the water heater at periodic intervals. Doing so will make sure that the heat exchanger stays in optimal condition and it’ll last for a long time.

What Tools Do You Need To Flush Navien Tankless Water Heater?

You’ll need to have some tools to carry out the flushing procedure smoothly. Here’s a quick look at everything you’ll need for this job:

  • A Phillips screwdriver to remove the screws holding the front cover of the water heater in place.
  • A bucket that’s at least 5 gallons or larger to store the cleaning solution.
  • A water recirculation pump to circulate the cleaning solution to the heat exchanger.
  • A cleaning solution diluted with water.
  • 3 different garden hoses as they’ll have to be attached to the pump and the water lines of the heater.
  • A toothbrush or cloth to clean some components that you’ll remove during the flushing process.

On top of that, it’d also be nice to have Teflon tape so that you can create a perfect seal when restoring the water lines. You’ll also need a pair of channel locks to remove the filters. You may need wrenches depending on the model of your water heater to turn the water lines on and off.

navien tankless water heater flushing tools

So, that’s all you need to carry out the flushing procedure. It’s important that you arrange all these things. Otherwise, you’ll be in trouble if you don’t have anything when you’re flushing the water heater.

What Is In A Navien Tankless Water Heater Flush Kit?

You’re not likely to have tools like a recirculation pump and a cleaning solution if you’ve never flushed your water heater before. So, you can look into a flushing kit in that case. You can find it easily in any hardware store that’s close to your location.

descaling solution of navien tankless water heater

A flush kit normally has a recirculation pump, a cleaning solution, a few hoses, and a bucket. So, you’ll find almost everything you need there. It’s also not too expensive as you can easily find such a kit within $150 or less. So, make sure you have the tools ready before you flush the water heater.

How To Flush Navien Tankless Water Heater [Fully Explained]

Flushing the water heater is an easy process. If you’re intimidated by it, you’ve got no reason to worry. Trust me, I’ve done it multiple times and I can tell from my own experience that anybody can do it.

All you need to do is to follow my instructions carefully. I’ve broken down the entire process into simple steps. You can easily keep up with them. So, here are the steps you should follow to flush your Navien water heater:

Step 01: Remove The Front Cover

Turn off the electrical power to the water heater by pressing and holding the power button. Then, unplug the connection of the water heater to the power outlet just to be extra safe.

Next, shut off the gas supply to the water heater as well. Turn the gas control valve so that it’s perpendicular to the gas lines to turn off the gas supply. Turn off both the cold and hot water lines in the unit.

Remove the four screws holding the front cover of the water heater in place. Once you remove them, you can pull out the front cover and look at the internal components of the water heater.

Step 02: Clean The Air Intake Filter

The air intake filter makes sure that only clean air is used for combustion. It stops little specs of dust and bugs from getting into the heater. But in the process, the air intake filter gets dirty. So, you have to clean it.

You’ll find it right at the top of your water heater after you remove the front cover. You’ll see that it’s secured in place by a screw. Remove that screw to loosen the air filter. You’ll have to loosen another screw at the top of the air intake. Once you do that, you’ll be able to pull out the filter.

If there is any dirt, you can blow it out of the air filter. If there are more stubborn pieces of dirt, then you can clean the filter by using running water. You can even use a toothbrush to get the dirt out.

cleaning the air intake filter of navien tankless water heater

If you get the air filter wet, make sure that it gets completely dry before you put it back in. Otherwise, an error code will come up on your water heater. Once you reinsert the air intake filter, you can put the front cover of the water heater back on.

Step 03: Drain The Water Heater

Locate the main cold water inlet and hot water outlet valves at the bottom of your water heater. They’ll be colored blue and red respectively. Turn them both off if you haven’t already done it.

cold & hot water valves of navien tankless water heater

Remove the cap on the cold water service port of the cold water side. Then, attach one end of the garden hose to it. Place the other end of the hose in a bucket or where you want to get rid of the water.

Similarly, take another hose and attach one end of it to the service valve next to the hot water valve. The other end will go to the area where you want to drain the water.

You can just hand-tighten the garden hose to the valves. There’s no need to use wrenches or anything like that. Turn on the hot water faucets in your house. Then, you can turn on the service valves to release the water.

The water will automatically start draining. Pull the PRV so that the water heater can continue to drain the water and maintain the pressure as well. Once you’ve drained the water, close the PRV.

Step 04: Clean The Water Inlet & Recirculation Filter

If you want the flushing to go smoothly, it’s a good idea to clean the water inlet and recirculation filters. Both of them are located at the bottom of your water heater. You can use a pair of channel lock pliers to pull them out.

Before you remove the filters, place a bucket under them to catch the water coming out of them. If there’s any dirt in any of these filters, you’ll have to clean them with running water.

You won’t have a recirculation filter if you don’t have a Type A model. In that case, you only need to clean the water inlet filter. Once the filter is clean, you can put it back in and tighten it with the channel lock pliers.

recirculation & water inlet filter of navien tankless water heater

Similarly, pull out the retaining clip to loosen the condensate trap while placing the bucket under it. Clean it if it’s dirty and reinsert it into the water heater. Then, restore the retaining clip to secure it in its place. Make sure you don’t lose the O-ring in this process and that it’s seated correctly.

Step 05: Descale The Heat Exchanger

Connect the free end of the hose connected to the cold water service port to the recirculation pump. Then, place the pump into the bucket and pour the cleaning solution in there.

Then, you can turn on the recirculation pump. The cleaning solution will go into the heat exchanger and start descaling it. The cleaning solution will come out of the free end of the hose connected to the hot water service port.

Let the recirculation pump run for at least 30-45 minutes so that the cleaning solution is circulated properly. Once that time has passed, you can turn off the pump as the descaling process has been completed.

Step 06: Purge The Cleaning Solution

Once the descaling is done, you need to get the cleaning solution out of the system. Turn off the cold water service valve and remove the hose connected to it. Then, put the cap back on.

Turn the cold water valve so that the heater gets supplied with clean water. You’ll notice that the cleaning solution and water will start coming out of the free-end hose connected to the hot water service valve.

Continue this process until your bucket gets filled with the cleaning solution and water. Then, you can disconnect the hose and the pump and set them aside. Turn off the hot water service port as well and get rid of the solution you have in the bucket.

Then, place the bucket where it was to do another round of cleaning. Turn on the hot water service port and wait until the bucket gets filled again. Once that’s done, turn off the hot water service port again and remove the hose connected to it.

Step 07: Finishing Touches

Turn on the hot water faucets and let them run for a few minutes to get rid of any cleaning solution residue. Then, plug the heater into the power outlet, and turn on the hot water valve, and the gas supply.

Restore the power supply to the water heater by pressing the power button. Then, let the heater run for a while. Eventually, the cleaning solution will completely go away and you’ll be able to use your water heater again.

How To Flush A Navien Tankless Water Heater With Vinegar?

If you don’t want to use a cleaning solution, that’s completely fine. You can use food-grade white vinegar for this job. The entire flushing process will be the same. The only difference is that you’ll be using white vinegar instead of a cleaning solution in this procedure.

It’s pretty safe if you use 2 gallons of white vinegar and dilute it with a little bit of water. You’ll notice that the color of the vinegar will start to change as it circulates through the heat exchanger.

That’s a great sign as it means the flushing process is working perfectly. Let it run for 30-45 minutes to descale the heat exchanger. Then, remove the hoses and restore the water heater to its original condition to continue using it.

How Often Should You Flush A Navien Tankless Water Heater?

The number of times you need to flush your tankless water heater depends on how quickly the heat exchanger gets dirty. The heat exchanger will develop a build-up of sediments in it as you use your water heater.

As you know, the primary reason behind flushing the water heater is to remove the sediments from the heat exchanger. So, how often you’ll need to flush the water heater depends directly on the hardness level of the water in your area.

Generally, Navien and I recommend that you flush the water heater at least once every year. But that’s just a normal guideline. You may have to do it more often if you live in an area that has a hard water supply.

You’ll have to do a little bit of trial and error to figure out the right flushing frequency for your water heater. After you flush your water heater for the first time, do it again six months later.

If you don’t see a lot of sediments coming out, then you can do it once every year. But if you see a decent build-up of sediments, you can continue flushing every six months.

Remember that there’s no harm in flushing the heat exchanger more often. But if you do it less than required, your heat exchanger can get damaged early on.

Having said that, flushing too often isn’t harmful to your water heater. But it’d be a waste of your energy, money, and resources. So, take your time to figure out how many times your water heater needs flushing and act accordingly.

How To Maintain A Navien Tankless Water Heater?

Flushing the heat exchanger is the most crucial thing you can do to extend the lifespan of your water heater. But there are many other things you can do along with them to further improve the condition of your water heater. You can do these things to maintain your water heater properly:

  • Clean the exterior of the water heater and the area around it.
  • Check if the air filter is dirty from time to time and clean it with a toothbrush to get the dirt out.
  • Drain the condensate water in the siphon.
  • Protect the water heater from being frozen when you’re going on a vacation.
  • Clean the water inlet filter and the recirculation filter.

If you follow the maintenance tips shared above, there’s no reason that your heater can’t outlast your home. If you want detailed information on how to follow these steps, I have compiled a dedicated guide for you. Check out my guide on maintaining Navien tankless water heater to learn more about it.


How long will a Navien tankless water heater last if you flush it at the right intervals?

If you flush the water heater correctly and you maintain it well, the water heater can last for even 30 years. In some cases, it can even last longer than that such as 35-40 years.

Why are Navien tankless water heaters so efficient?

Unlike tank-style water heaters that keep heated water all the time, tankless water heaters only heat the water when it’s needed. That’s why they’re much more energy efficient compared to the tank-style heaters.

What to do if you live in an area with a hard water supply?

The water supply in your area should meet the National Secondary Drinking Water Regulations to ensure proper operation of the water heater. If you live in an area with a hard water supply, you can use a water softener.

How soon will the heat exchanger in your Navien tankless water heater get damaged if you don’t flush it?

If you don’t flush the heat exchanger properly, there’s no doubt that it won’t last a long time. A heat exchanger that hasn’t been flushed at all can fail in as little as 8 years.


How to flush Navien tankless water heater? Now, you should know all about it after completing this guide. Remember that flushing a tankless water heater is a simple procedure. So, there’s no need to panic about it.

Hopefully, you’ll find this guide on Navien flushing instructions easy. If you flush the water heater along with following the other maintenance practices, it’ll surely last a long time. Check out my guide on why a Navien water heater runs constantly in case you’re facing that issue and want to learn the fixes.

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