Before knowing how to flush a tankless water heater, you should know the importance of it. Do you know why it is essential to flush a tankless water heater?  Since we know that tankless water heater will build up sediments such as calcium and debris and maybe the filter inside the unit. Thus, these sediments have to flush out possible with food-grade white vinegar for up to 12-18 months.

You have to maintain it to get peak performance. For this purpose, you have to clean the air filter to improve efficiency. That’s the reason we are here with you. We will provide you every detail on how to flush a tankless water heater. Here are flushing steps for both electric and gas tankless water heater.

Preparation for Flushing a Tankless Water Heater

Regardless of whatever your appliance is, it requires maintenance. As far as the electric tankless water heater is concerned, you have to keep your system clean to peak performance. Here we will provide you some easy steps that you need to follow when you will flush an electric tankless water heater. Before going into steps, you should get your supplies together. But make sure that you know about all the safety precautions.

The first thing is that you always use caution before you start working with your tankless water heater. It might be possible that the water in the water heater can be hot.

The next thing is that you don’t have to recommend that you don’t use chemicals strongly. Its alternative is vinegar that is safe and effective to use. Not only that, it is more friendly to the environment.

Last but not least, you should always check the user manual. It is because each model requires some specific instructions that you have to follow before flushing.

Necessary Supplies

It would be best if you kept in mind that both electric and gas-electric water heaters require some equipment for flushing. It may be different or not; it depends on the model. Unlike a gas tankless water heater, the electric tankless water heater is easy to use. Some require only a screwdriver and wrench, but some require more essentials. However, gas systems are complex to flush, and you need these things.

  • 5-gallon bucket
  • Screwdriver
  • Adjustable wrench
  • Needle nose pliers
  • Non-contact voltage tester
  • Submersible pump
  • 6 ft washing machine hoses 
  • 4 gallons of virgin
  • Food grade white vinegar

Some brands offer Isolation valves with service ports when it comes to flush a gas water heater. While many of the brands need a plumber who is doing the installation. However, lots of gas tankless water heater does not come with isolation valves with service ports. Then we highly suggest you call a plumber for the installation. It would be worthwhile for best bangs for bucks that won’t regret.

Here is an important note for you, electric heating water systems are entirely different compared to gas tankless water heaters, unlike gas tankless water heaters.

Deliming Solution

Most of the commercial solution models come with removable limescale build-up. On the other hand, lots of brands come with vinegar. We already have told you that vinegar is safe, effective, and environmentally at less price.

When you have the supplies and tools, and precautions in mind, you can flush an electric tankless water heater.

Check out the list of 11 Best Tankless Water Heaters

How to Flush An Electric Tankless Water Heater

The electric tankless water heater may require some disassembly. It is a bit different from a gas tankless water heater. For instance, the navien brand offers straightforward steps to deal with the water control valve, while the Takagi brand requires additional steps.

Here are some simple and effective steps that we have broken down into three phases.


  1. At the same step, you need to shut off the electrical power at the breaker.
  2. Next up, you have to close the cold water shut-off valve.
  3. Tap to run the faucet so the water will drain from the hater.
  4. When it is done, you have to shut off the valve of the hot water.
  5. You have to make sure that there is no longer power leading to the terminal. For this purpose, you have to stop the access panel and use a non-contact voltage tester. Not only that, but you should also unscrew. In this way, it secures the wires to the heating elements.
  6. Now it’s time to loosen the hexagonal brass top of the heating element. Make sure you are losing it in a counter-clockwise direction. This way saves your heating element.
  7. If you notice any crack or any sign of damage, then you should inspect the heating element immediately.
  8. The last thing is that you have to store it in the copper chambers of the heater so it can be cleaned thoroughly.


  1. Now it’s time to fill the cooper chambers with a virgin. It is better to get food grade white vinegar.
  2. After that, you have to wait 90 minutes to 2 hours maximally. The vinegar allows a break of a scale on the elements. Then drain the vinegar.
  3. Replace the heating element and rescue the wires again.
  4. It’s time to open the cold water shut-off valve and fill the tank.
  5. Make sure that there is no leakage issue.
  6. You can also use the paper towel test for it.
  7. After complete satisfaction, you need to open the hot water shut-off valve.
  8. Lastly, you have to turn on several hot water faucets and flush the water for about 5 minutes until it pops out all the vinegar.

Clean Up

When it comes to the cleaning process:

  1. First of all, you need to turn off all hot water faucets and the cold water shut-off valve.
  2. For the replacement of filters, you have to remove the cold water inlet filter, and you have to flush it under cold water to rinse all the dust and debris.
  3. Lastly, close the access panel and turn the power on. That’s all.

How to Flush a Gas Tankless Water Heater?

It takes lots of care when you flush the gas tankless water heater. Hence you have to check the user manual before flushing a gas tankless water heater because you need to get instructions to flush and descale. Regardless of the brand, there are some simple flushing steps that you need to follow.


  1. The very step is to disconnect the electrical power going to the heater. Then you have to eliminate the access panel.
  2. Then you needed a non-contact voltage tester. It will make you sure there no more power is coming to the terminal. After that, you need to close the gas isolation valve.
  3. Not only that, you have to locate the hot and cold shut-off valves.
  4. This feature prevents the water back into the system.
  5. When it comes to the hot water pressure, you have to relieve its valve along with the hot water line since it is not hot. Both ports are available there to connect the hose.
  6. Not only that, you have to place your submersible pump (as recommend 5-gallon bucket)
  7. Make sure the pump of cold water is connected with the hose safely.
  8. You have to pick the hose of hot water into the bucket.
  9. Lastly, you have to take 4 gallons of vinegar into a bucket.


Let’s discuss the flushing when it comes to a gas tankless water heater.

  1. Turn the pump on by opening the hot and cold service.
  2. Now you have to allow the vinegar to circulate in the heater for up to 60 minutes. This process will eliminate the scale and sediments by flushing them out.
  3. The next thing is to turn the pump off and dump the vinegar.
  4. You have to remove the hose and shut off the cold water service port.
  5. It’s time to tap hot the cold water valve and flush the remaining vinegar using its hose.  Make sure every drop drop-off and close it.
  6. Lastly, please take off the cold water inlet filter and hot water in-line filter and rinse it to make sure all sediments are removed.

Clean Up

  1. Lastly, you have to replace the filter in an appropriate way.
  2. Open the cold as well as hot water shut-off valves.
  3. In this stage, you have to replace its access panel.
  4. Turn on the gas shut-off valve.
  5. And restore the electrical supply.

How often should a tankless water heater be flushed?

It is challenging to flush a tankless water heater. It keeps the system efficient to get high performance. However, before flushing the tankless water heater, you have to read the recommendations. Regardless of the tankless water heater brand, it would be flushed every 12 months.

To flush the tankless water heater, it is very different, unlike a tank water heater. But whether it is a tank or tankless, both have been negatively impacted by limescale build-up. So you have to clean it because it would be unhygienic to health and later quite expensive.

Impact of Hard Water

First of all, you need to know the hardness level of your water supply. You need to flush out the frequency so the mineral content will be removed. If you have a high mineral content in water, it will increasingly develop more limescale build-up. Not only that, if you are living in hard water, then you have to care more to get clean water.

When it comes to the tankless water heater, they use a heat exchanger to hot the water. That’s the reason that heat exchange is sensitive to limescale, and a small amount negatively impacts its performance and efficiency.


If you don’t clean your tankless water heater, then the limescale will build up over time. It increasingly develops in the heat exchanger and decreases the efficiency of the system. That’s why you need to know how to flush a tankless water heater.

Not only that, when the heat exchanger gets heating up with scale, it as to work hard to improve the water quality. This only doesn’t lowers the efficiency of water but also its lifespan. To get the ultimate performance, you need to flush the water heater.

Here is one thing that you need to know is that most of the brands don’t cover the damage caused by limescale build-up. Since you have to maintain it to decreases causes of lowering the performance. Hence, it makes it critical to be proactive when you know how to flush a tankless water heater.

Besides that, brands are always trying to put their efforts best as much as possible. They are looking for ways how to improve the products and help reducing limescale build-up. Hence, it is better to flush the tankless water heater prior to the scale build-up.

Importance of Reading User Manual

Checking out the instruction manual will ease your work. Since it is critical to flush the electric or gas tankless water heater and you need to know lots of things so you can flush all scale build up properly.

However, if you don’t flush properly, then it will damage your unit, and you will get less performance of purification. That’s why we strongly recommend you to read the instructional manual before flushing a tankless water heater.

FAQ – Frequently Asked Questions

Do tankless water heaters need to be flushed?

With time, either you have an electric or gas tankless heater, it causes mineral build-up. This will later decrease the efficiency of purification as well as the lifespan of the unit. Thus, you need to properly maintain and clean or flush your tankless water heater regardless of which type you have. We strongly recommend you flush your unit once in 12 months.

Final Words

All In all, we hope you have found an answer to how to flush a tankless water heater. These are simple steps that you need to know before making a purchase. Besides that, if you have any questions, we are here to help you. Thank you for visiting us!