How To Descale A Tankless Water Heater

It is important to descale the tankless water heater at least once a year. The hard water forms the calcium deposits, dissolved at a high temperature. 

And on a tankless water heater, the downdraft venting is used to remove vaporized gas from the unit. If this venting isn’t working correctly or is blocked, you may need to clean or descale your unit.

Regular maintenance will help to avoid any damages that the scale buildup may cause.

The first step is to remove any loose scale with a scraper, brush, or sponge. And the following step is to mix up some citric acid solution in a bucket of hot water and pour it into the tankless water heater. 

You should wait for at least 10 minutes before you try to flush out the solution. Clean any residue from the heater after you have flushed out all of the citric acid solutions with clean, warm water and dry it off with a towel.

Keep reading to get an in-depth guide on how to descale a tankless water heater. 

How To Descale A Tankless Water Heater

Why Do The Tankless Water Heaters Need to Be Descaled?

A tankless water heater draws in cold water from a nearby source, heats it on-demand, and then supplies hot water to you before returning the cold water to the source.

Tankless heaters are more expensive than traditional tank-type water heaters, but they have fewer drawbacks. Tankless systems can save more money on your monthly utility bills since they don’t store heated water in a large tank.

If you use a tankless system for your home or business, it is essential to maintain it properly by descaling the unit every six months. 

This is because, over time, scale deposits will build up inside of the unit and can decrease efficiency and shorten its lifespan if left unchecked.

Complete Guide On How To Descale A Tankless Water Heater 

The process of descaling a tankless water heater is pretty easy and straightforward. And now all the things you have to do is prepare the tankless water heater for descaling, flush it with vinegar, then flush it with either citric acid or sodium bicarbonate solution.

You can get the necessary equipment from the hardware store. You just have to prepare an open-top container, a bucket, a funnel, and a hosepipe for this task.

In order to descale your tankless water heater in the best way possible and in the safest way possible, you should always make sure that you follow the instructions given below:

Things You Will Need

Before you start to descale your tankless water heater, there are some things that you will need. 

First of all, you will need a water bucket. A 5-gallon water bucket will be perfect. You will have to use this bucket to collect the water. Next, you will need distilled white vinegar. Make sure you have around 4-5 gallons of vinegar. 

Often people do not understand what kind of vinegar to use. Standard food-grade vinegar works fine as it is not too harsh. The vinegar will break down the scale on the tankless water heater. Apart from that, you will also need connection drain hoses and a pump that can be submerged in the water.

You can buy all these from the nearest store, or you can get yourself a descaling kit that will provide you with all this. The flushing kits will contain everything you need starting from the bucket, hose, pump, and descaler. 

Part 1: Prepare Your Tankless Water Heater

Turn Off The Power

Preparing your tankless water heater is the first step. 

Begin by turning the power off for the heater. You check whether the power is off by removing the access panel using a voltage checker. 

Locate The Valves And Close Them

Before going further, you need to locate the isolator valves on your water heater. Most of the time, the red-colored isolator valve will indicate the hot water, whereas the blue-colored isolator valve will indicate the cold water.

Once you locate the valves, turn them off for both the hot and cold sides. Next, you will have to find the drain caps and take them off. 

Take your five-gallon bucket and put it below the hot water part. If there is a drain valve, turn it on to drain any excess water. Repeat the same steps for the cold waterside.

Connect The Hose With The Pump

Please take out your submersible pump and connect your hose to it. Once the pump and hose are combined, put them into the 5-gallon water bucket. Next, you will connect the hose with the cold water and hot water service port. 

Finally when everything is ready to go, pour your white, distilled vinegar into the bucket. It is recommended to use a minimum of 4 gallons of vinegar in the bucket.

Part 2: Flush Out Your Tankless Water Heater

Turn The Pump On

Turn your pump on and let it do its magic. Keep it on for an hour, depending on how much water your pump can run through per minute.

The vinegar will break down the scale and remove any other impurities. If you see the water is getting cloudy, you can change the vinegar solution after 30 minutes. 

You should turn the pump off and throw the vinegar solution.

Disconnecting The Hose

In order to disconnect the hose, turn the cold water service port off and remove the hose that is attached to the cold water service port. Close the cold water main valve and replace the hot water drain pipe in the empty bucket. 

 Once all the water has finished draining, turn off the cold water valve. Lastly, close the hot water service ports and remove the second hose. 

To disconnect the hose, turn the cold water service port off and remove the hose attached to the cold water service port. Close the cold water main valve and replace the hot water drain pipe in the empty bucket. 

Then, turn on the cold water valve. This process will clean the heater by flushing it with cold water and will remove the excess vinegar. You should flush for at least five minutes or until the heater has been filled with 20 gallons of water.

Turn off the cold water valve once all the water has finished draining. Lastly, close the hot water service ports and remove the second hose. 

Part 3: Clean Your Heater Thoroughly

Clean The Filters

If you want to give your tankless water heater a thorough cleaning:

  1. Do not forget about the filters.
  2. Please take out your water filter and then clean it gently under running water to remove any dirt.
  3. Put the filters back in and open up the hot water and cold water main valves. 

Turn On The Power Supply

Once you have cleaned the filters, assemble the access panel, connect the electrical supply, and turn on the power supply.

How Often Should You Descale Your Tankless Water Heater?

All electrical appliances require regular maintenance. Similarly, when it comes to your tankless water heater, the same rule applies to it as well. 

It is recommended to descale your water heater after three years of installation. From then on, how often you descale your water heater will depend on the amount of sedimentation your heater produces.

After the first flush, if you find sedimentation, you have to descale it again after three years. However, if you see no sedimentation, you can descale it after five years.

Apart from that, factors like hard water will also influence how often you descale your heater. If you are a resident of an area with hard water, in that case, you need to descale your heater regularly. 

If you do not know about the water quality in your area, you can take help from your city government. Or a plumbing professional can also make your job easier for you.

Take Help From A Professional 

Tankless water heaters are generally used by those who live in an area without access to municipal water.

Unlike the traditional tank-based models, these units don’t need to be drained of water or refilled after use. This means that they consume less energy and provide all-around better performance. However, like any other appliance, they will need periodic maintenance and care.

One such task is tankless water heater descaling.

Depending on both the manufacturer and model of your tankless water heater, you may need to descale it once every two years or once every six months on average. 

The process involves running vinegar through the unit for a set period to remove calcium buildup from within its pipes.

As a beginner to the task, you might feel nervous or confused. So it is better to take help from a professional for descaling your tankless water heater safely.


The tankless water heater has been a blessing to many. With regular maintenance, your tankless water heater will go a long way. 

People often wonder how to descale a tankless water heater, and the process is straightforward. With just a few twists and turns of the valves and some tools, you can easily descale your trusty tankless water heater and stay worry-free throughout the years.

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