How To Descale A Tankless Water Heater – Step by Step Guide

Tankless water heaters have proven to be the most efficient water heating units in recent times. These units last longer with lower running and maintenance costs. Those who have these units installed in their homes must have got this question popping up in their minds often how to descale a tankless water heater?

Well, the process is pretty easy and you can do it yourself at home by following some simple sets. But we recommend getting it done by a professional plumber to avoid getting into any trouble.

The tankless water heating units have proved to be very helpful for fulfilling daily hot water needs. These compact units can fit into any small space. A tankless water heating unit can last for about 20 years with proper maintenance.

The process of descaling or flushing the tankless heating unit is simple and can be done by the user himself at home. It’s important to know how to perform the descaling procedure.

Why do Tankless Water Heaters Need Descaling?

Tankless water heaters need a lesser amount of energy to work as compared to the previous units. They are also less space occupied which is a helpful feature for those already living in small spaces. They do need maintenance like all other devices but once a year.

This annual maintenance prolongs the life of the unit. This is the reason why it’s recommended to descale the unit every now and then. To be able to do the process of how to descale a tankless water heater properly you just need to follow the above process that we have discussed in this article.

Process of Descaling a Tankless Water Heater

Is your water heating unit installed in a wall? To give the unit access to water and other pipes it is installed in the wall. To descale such a unit you might need to take help from a professional plumber. The presence of a professional makes the task much easier. If you are eager to do the process yourself then here is what you need to get started and get it done.

Before starting the descaling process please cut off the electric or gas supply to the heating unit. Also, make sure to stop the water supply to the heater. Make sure to remove the caps from the service valves as well.

Equipment Needed to Start the Process

  • 2 hosing lines
  • White vinegar
  • Bucket
  • Accessing the unit

Some tankless water heaters have an outside covering to protect the connections. This covering needs to be removed in order to access the unit for descaling purposes. Some units don’t have such a covering.

Check for flushing valves

Tankless water heating units have flushing valves installed. Check your unit for these valves. If you are not able to find them then call your local plumber and ask him to get these installed for you.

Cutting off the gas supply

If your tankless water heating unit is fueled by gas then you need to cut off the gas supply first. This involves turning the valve perpendicular to the fuel supply. This step is most important to avoid any hazards during the descaling process.

Disconnecting the water supply

Disconnect the water supply by turning off the water supply valve. Disconnect the cold water valve that supplies cold water to the water heating unit for heating. Also, disconnect the hot water valve that supplies water outside through the faucet for daily use.

Connecting the hoses

Remove the caps present on top of your flushing valve. This helps remove any built-in pressure. Connect the hose tightly to the flushing valve. Make sure the connection is tight enough so the detergent solution won’t leak out. Rubber washers are used to prevent such leakage.

Turn the flushing valve on by rotating it to a perpendicular position to the hot and cold water valve. Close the output water valve and instead turn on the purge valve. Choose the correct hose line.

Filling bucket with a cleaning solution

Put the vinegar or detergent solution in a bucket and use the pump to circulate the cleaning solution through the water heating unit. Carry on this process for 30 minutes if you have a cleaning solution or for 3 hours if you are using vinegar to descale the water unit.

After you have completed the mentioned time now get a bucket of clean water. Use the same pump to circulate the water through the pipes. Keep pumping this clean water into the pipes until the returning water also becomes clear. When the water returning from the unit is clear discard the remaining cleaning solution.

Cleaning the sediment filter

A sediment filter is present on the cold water inlet to prevent the water sediments from reaching the heating element. The solids can build up inside the sediment filter. Unscrew the filter and use a brush to thoroughly clean it. The presence of sediments inside the filter hinders water flow through the inlet valve.

Reconnecting water and fuel supply

Disconnect the hosing line from the water heater and close the purge valves of the unit. Make all the connections again and connect your unit to the water supply again. The unit is ready to heat the water up to the required temperature.

Here is the video showing the process of flushing a tankless water heater:

How to Flush a Tankless Water Heater With Vinegar

Tankless water heaters are often prone to scaling mainly due to the accumulation of calcium salts that might be present in the water. This can significantly impact their overall performance and might affect their ability to heat the water immediately. Therefore, it is important to clean these tanks on a regular basis to maintain their efficiency in the long term.

Over the years, various materials and chemicals have been used to descale and flush out tankless water heaters. However, vinegar has always maintained its position on the top because of its acidic nature, which can easily break up the sediments without damaging the stainless steel of the heater, which might be affected because of other chemicals.

In this article, I have developed a step-by-step guide on how to flush tankless water heater with vinegar to help you clean your product on a regular basis.

How Often Should You Flush a Tankless Water Heater?

The requirement for flushing out the tankless water heater is highly dependent on environmental and physical factors. On average it is important to flush your tankless water heater once every year to maintain its efficiency and prevent it from getting damaged in the long term.

However, this is not the case for the majority of the users as the hardness of the water that is being used for the heating purpose can significantly impact its performance and can lead to varying degrees of scaling.

Areas with high hard water content can lead to increased levels of salt accumulation and might require frequent flushing as compared to areas where soft water is available in abundance. So, it is important to identify the composition of the water available in your area and the level of accumulation caused by it.

Then depending upon the condition you can flush the tankless water heater twice or thrice a year.

You might have to clean the system frequently i.e. more than three times a year if there is excessive scaling, which is interfering with the normal performance of the water heater.

Similarly, you can also use water softeners or filters to separate large salt deposits from the water and reduce the overall hardness of the water, which will in turn decrease the salt accumulation inside the heating chamber and will reduce the requirement of cleaning them repeatedly.

What are Isolation Valves?

Isolation valves are one of the most important components inside a tankless water heater and are often used to cut off the supply of water or gas in certain areas of the pipe. This is highly essential if you want to control the supply of water in some areas.

The majority of the isolation valves are often confused with the shut-off valves that also serve a similar purpose. However, you will find isolation valves installed in many areas around the house to control the supply of water and gas.

There are two basic types of isolation valves present in the market these days. These include those with rotatory motion featuring a butterfly or ball valve and those with linear movement. The latter contains the diaphragm valves and is highly popular among consumers.

Similarly, it isn’t necessary that an isolation valve is installed with your heater, however, we highly recommend installing one for the best results.

All of this highly depends on the design as well as the technician installing the heater at your home. If you observe that there isn’t an isolation valve installed with your tankless water heater, we highly recommend installing one to get the best results. This is because it can serve as an important security feature especially when you are cleaning and need to flush out excess water or cleaning agents.

Flushing a Gas Tankless Water Heater


The preparation steps involve preparing yourself and the heater for the long cleaning process. It must be carried out properly to avoid any accident during the cleaning and ensure that you are also safe from accidental harm. For this purpose, first, you should disconnect and power off any electrical supply that might be reaching the water heater.

Switching off the heater will eliminate the potential risk of power shortage and will keep you safe. Afterward, remove the access panel as well. You can also monitor the incoming voltage using a power tester to make sure that the power is properly disconnected.

Besides this, you should also locate and close the isolation valve alongside the identification of the valves of hot and cold water.

Once you have located the hot water valves open them to release any unwanted pressure. Furthermore, connect the hoses to the ports of hot and cold water. Use the cold water hose and connect it to the pump and keep the pump in a large bucket. Then prepare four gallons of food-grade vinegar and add it to the bucket.


The next step involves the opening up of both hot and cold water ports alongside the pump. This allows the vinegar to circulate properly into the heater. Keep the vinegar in the heater for a minimum of one hour. You can also keep the vinegar longer if your heater is large or if there is an excessive accumulation of salt.

Once you observe that the sediment has started to break, release the pump and dump the vinegar. Then, close the cold water port and remove the attached hose from this side.

Then again open the cold water port and let any remaining vinegar flush out from the system. This will ensure that your heater is thoroughly cleaned in the process.

Again close the cold water hose and let the water flush out properly, then disconnect the second hose as well.

Then disconnect both cold and hot water in-line filters and wash them thoroughly under clean water to eliminate any residual sediments that might be trapped in those filters.

Clean up

The third and last step involves assembling the whole unit together and cleaning all the unwanted and dirty components. This includes cleaning the filters thoroughly and removing the excessive sediments.

Once the filters are clean you should insert them back inside the heater and securely open the hold and cold water valves. After you have opened the valves, it is time to replace the access panel and open the gas valves that were previously shut down in the preparation phase. Then reconnect the electric supply and you are good to go.

Flushing an Electric Tankless Water Heater


The preparation step in an electric tankless water heater is different and can take considerably longer time as compared to that of a gas tankless water heater. You need to start by shutting off the power supply by switching off the power breaker.

Then you should close the valves of hot and cold water and open the faucet to drain off any excess water that might be present in the heater.

Then, afterward, remove the access panel to disconnect the voltage properly. You can also use the voltage tester to identify whether the voltage is still present in the system or not.

Then it is time to disconnect the heating wires present in the system, which can be carried out by unscrewing the screws present in the surrounding.

Then move the brass top in the counterclockwise direction to remove the heating element and expose the interior of the heater properly. You can also place these heating elements in the cooper of the heater to clean them along with the heater itself.


During the flushing stage, you should fill the copper chamber with the undiluted food-grade vinegar and let it sit inside for up to two hours. This will completely dissolve the excessive sediments that might have clogged the heater.

After you observe that the salts accumulated inside the heater have started to descale, open the drainage and let the vinegar drain properly.

After you have completely drained the vinegar from the system, it is time to secure all the wires back into the system and replace all the heating elements. Then open the cold water valve that you had previously shut off and let the tank properly fill with water.

During this stage, it is important to identify if there is any leakage in the system. If you observe that the system is properly secure and there is no leakage, then you can open the shut-off valves of hot water.

We also recommend opening the hot water faucets to let the chamber and the tank properly fill with the hot water. This will help in the removal of any remaining vinegar from the system and will clean the tank thoroughly and properly. Also, check for any air pockets in the system and clear them properly to avoid any trouble in the future.

Clean up

Once you have cleaned the system and have successfully removed the excessive vinegar, close all the hot water taps and ensure that there is no leakage. Then, shut off the cold water valve and remove the cold water inlet filter. Removing the cold water filter will let you know if there is any clogging in the system.

If you observe that the filters are clogged, wash them properly under cold water to eliminate the clogging. This will remove all the debris from the system and will clean the filters properly. After you have cleaned the filters, reinsert them back inside the heater and close the access panel. Lastly, turn the power on and the procedure is complete.

Why Opt for Professional Help?

If you are not able to properly descale the unit you might end up leaving harmful chemicals that will mix with the drinking water. The presence of harmful cleaning chemicals in your drinking water will make the water harmful to your health.

At other times you might forget to turn on a valve which also results in improper functioning by the unit. You will need to disassemble the unit again and then properly clean any leftover cleaning solution. To avoid any such discomfort from occurring you can ask a professional plumber for help. They will provide a quality service at an affordable price.

Air Filter Maintenance

Uncover your water heating unit to access the air filter. This filter is mostly located on top of the water heating unit. Once you know where the water heater is remove it to look for any dirt that has built up inside it. Use a soft brush with a soapy solution and a piece of cloth to clean it.

Once all the dirt is removed use clean water to wash away the cleaning solution. Use a cloth to pat the filter dry. Let the air filter dry in the open air and then place it back into the unit.

Cost of Descaling a Tankless Water Heating Unit

Self Cleaning a tankless water heating unit is an easy task. It is not an expensive process at all. You need to know some basics about your water heating unit and the process will become easy peasy for you. If you want to get professional help from a plumber then this process might become a little expensive for you. Doing the descaling job yourself will save you a lot of money.

Once you have gathered all the necessary equipment next you need to be ready to invest about 2 to 3 hours into the process. Although this is an easy process yet it will take a considerable amount of time to get done.

Reason for Scale Build-up in a Tankless Water Heating Unit

If you are replacing a traditional water storage unit with a tankless then you will be already familiar with the need of flushing the unit every now and then to prevent sediment buildup. The traditional water heaters are also prone to damage resulting from mineral buildup.

This buildup can lead to an explosion too. In the case of a tankless water heating unit, the build-up won’t result in an explosion but irreparable damage of some parts might result.

The heat exchanger is the most sensitive part of your water heating unit. If the sediment builds it will lead to more energy requirements for heating. And the limestone buildup ends up permanently destroying the heat exchanger. Thus the whole unit becomes useless.

When to Descale a Tankless Water Heating Unit?

Once every year descaling is important for optimal performance by the unit. This will prevent the sediments from building up inside your unit and clogging the valves. The good news is if you have a soft water supply you won’t need to descale your unit that often. If you are still confused about how often you should descale your unit then ask a plumber to help you out.

Is the Annual Descaling of the Water Heating Unit Worth it?

Tankless water heating units have proved to be a better investment than the traditional storage-type water heaters. This is cause they have higher running costs. The initial installation cost of a tankless unit will be much higher but in long run the benefits of a tankless water heater out way the initial cost.

According to studies, these units are about 30 percent more energy efficient. The maintenance process is totally worth it cause if properly done it prolongs the life of the unit to about 20 years. High-level maintenance may help the unit last for even up to 30 years.

Frequently Asked Questions

Can I use vinegar to flush my tankless water heater?

Yes, you can clean the tankless water heater using vinegar because most often these products are often scaled because of the accumulation of calcium and other related salts. These salts are relatively difficult to remove and should be cleaned after 12-15 days using food-grade vinegar to avoid damaging the heater while keeping them clean throughout the day.

How long should you flush a tankless water heater with vinegar?

Cleaning the tankless water heater with food-grade vinegar is a common practice and is often adopted to clean the heater without damaging it. It is recommended to leave the vinegar inside the heater for at least one hour and then wash it off to remove and descale the stubborn salts that might be accumulated inside the system. You can also leave it a little longer for best results if you have a large heater.

Will vinegar damage a hot water heater?

No, vinegar does not damage a hot water heater especially if it is scaled. So, you can use it without any underlying concerns and keep your water heater clean in the long term. This is because the tankless water heaters are mostly made up of stainless steel which is long-lasting and does not get damaged easily even when exposed to intense chemicals such as acids in vinegar, thus, you can use food-grade vinegar to clean it easily.

Wrapping Up

If your tankless water heater has been clogged excessively and requires a thorough cleaning, then vinegar can be an ideal choice. The food-grade vinegar contains acetic acid, which is strong enough to break the sediments that might have clogged the interior of the heater.

At the same time, it is also mild in nature and damages the internal stainless steel surface of the water heater, which makes it a perfect cleaning agent.

Furthermore, the cleaning process is relatively easy and can be performed by closing the power supply and letting the vinegar sit inside the chamber for up to two hours. Once the sediment starts breaking, you can drain the vinegar and wash off the interior with water.

Then, properly clean the inlet filters with water and restore the default settings by closing the access panel and reconnecting the power supply. This will remove the sediment clogged in the heating chamber while keeping it new even after years of use.

With years of experience under his belt, Adam decided to put his water heater knowledge to work. By providing high-quality content and expert guides, Adam hopes to help anyone looking for expert water heater advice.