Descaling Tankless Water Heater

The process of descaling tankless water heater is usually only considered when there’s already a problem present.

Most people don’t even think twice about tankless water heater maintenance until it’s not properly functioning. But, contrary to popular belief, maintaining a tankless water heater is necessary to ensure its longevity.

The good news is – there are plenty of simple ways to resolve this problem. All you need are some supplies and the will to follow some straightforward steps.

So, without further ado, let’s get right into this topic!

Should Tankless Water Heaters Be Flushed?


Removing sediment, scale, and debris from a traditional tank seems to be common knowledge. From time to time, it’s necessary to flush the tank and improve its efficiency.

It’s true that tankless water heaters are in many ways more efficient than traditional water heaters.

Tankless water heaters require less space and turn out to be a cheaper long-term option. Not only are they more energy-efficient, but they are also less likely to collect scale.

However, they still need to be flushed from time to time to remove any limescale buildup. This is true both for gas and electric tankless water heaters.

The reason behind this is that tankless water heaters have no tank and, therefore, no space to allow some limescale buildup. In tankless heaters, scale attaches to the burners (or the heating unit) directly.

As a result of this, a few things can happen. First, the heater covered in scale will need to work more and spend more energy in order to heat the water.

This directly impacts not only the quantity of hot water but can also take a toll on your utility bills.

Lastly, this can also impact the water flow, as you will get reduced water pressure with limescale buildup inside the heater.

 Descaling Tankless Water Heater – When To Do It?

In general, it’s recommended to descale a tankless water heater at least once per year. If not used very often and by a great number of people, this can be reduced to every 2-3 years.

In some cases, even descaling the heater every five years will be enough.

However, descaling the tankless water heater once per year seems to be the best option for maintaining its functionality.

The very beneficial part of most tankless water heaters is the alert option they have. In other words, many tankless heaters will provide you with a notification of error when limescale starts to affect its function. If unsure, you can always consult a professional in order to assess the state of your heater.

Another thing you can do in order to postpone the cleaning of a heater is to install a water softening system.

Water softeners extend the life of tankless water heaters, and with that, you also save more money and energy. What makes water softeners so efficient is their ability to turn calcium and magnesium ions into sodium. [1]

Their purpose is to prevent the buildup of minerals in tankless water heaters, which is what creates limescale and bacteria.

Many other negative effects of hard water include dry skin and hair, faded or stained clothes, frequent plumbing issues, and much more. [2]

Supplies For Descaling Tankless Water Heater


If you’ve decided it’s time to descale your tankless water heater, first, you should collect all needed supplies.

The supplies you’ll need for descaling tankless water heater are:


  • A 5-gallon bucket
  • Submersible pump
  • Two connection drain hoses
  • Either white vinegar or a descaling solution


A 5-gallon bucket is needed for collecting the water and also for inserting the cleaning solution through the heater. For that to be possible, you will need a submersible pump.

Two connection drain hoses are what are needed to pull the water through the heater and rinse it. You need two drain hoses as there are both hot and cold water drain valves.

Finally, it’s up to you which cleaning solution you choose to flush the unit with. Some do it with white vinegar, and some do it with descaling solutions made specifically for this purpose.

Tankless Water Heater Descaler VS Vinegar


Speaking of a descaling solution, it’s often recommended to use undiluted white vinegar for this purpose. This is usually the case for Rinnai and Noritz tankless water heaters.

Most swear by the use of vinegar to flush the tankless water heaters. This is by far the safest and cheapest option for anyone looking for ways to descale a tankless water heater.

Some say that vinegar is actually not as effective at removing scale. Keep in mind that this is mostly false, and there are hundreds of articles showing the effectiveness of vinegar in cleaning.

However, there are still some surfaces that are better to be avoided when using vinegar as a cleaning solution. The story about vinegar being ineffective is probably made up in order to sell descaling solutions. [3]

This is why there are descaling solutions made specifically for the purpose to flush tankless water heaters. Nevertheless, if your tankless is in bad condition, it’s safest to choose the descaler and not vinegar.

Possibly the most famous one is the Flow-aide descaler. It’s non-corrosive and non-toxic and has proven to be very successful at removing water scales.

Water Heater Descaler Kit

If you’ve never flushed or descaled a tankless water heater before, chances are you don’t have the supplies mentioned.

No worries, as there are water heater descaling kits available on the market. A typical tankless water heater descaler pump kit usually contains:

  • A 3-5 gallon water bucket
  • Two hoses from stainless steel
  • A utility (submersible) pump
  • A cleaning solution

Depending on the descaler kit, the cleaning solution will be in powder or sometimes in liquid form. Such is the descaling solution of this Chromex Tankless Water Heater Flush Kit.

Descaling Tankless Water Heater – How-To

 Now let’s move on to the actual steps in descaling tankless water heater. Don’t be turned off by the many steps you have to take, as all of them are pretty simple to follow.

To descale a water heater, just follow these next few steps:

  1. Turn off the gas valve while keeping the unit turned on.
  2. Remove the drain caps on the water valves. This means you have to turn off both the red and the blue valve (for hot and cold water). The drain caps will be located on the left for the cold side and on top for the hot side.
  3. Then, place a five-gallon bucket underneath the blue valve and turn the valve on. This will drain any excess water still left in the heater.
  4. Repeat the same thing for the red (or hot water) side.
  5. Connect the two connection drain hoses to the submersible pump. Then, place that pump into a 5-gallon bucket. Keep the power cord away from the bucket!
  6. Connect the pump outlet hose to the cold water valve.
  7. Then, connect the pump drain hose to the hot water drain valve.
  8. Place the end of the drain into a bucket.
  9. Fill the bucket with three or four gallons of white vinegar or descaling solution. It’s very important that the pump gets completely submerged in the water.
  • On isolation valves, make sure to turn on both drain valve levers.
  • Turn on the pump – it’s now going to be working for at least an hour! Additional tip: you can change the cleaning solution after about 30 minutes to achieve maximum results.


It’s expected for your unit to try to fire up. It won’t do so anyway because the gas valve is off. It’s also possible it will show an alert that appears as an error code 11.

Don’t reset the unit anytime during the descaling!


  1. After an hour or more, you can turn off the pump. You should also close the cold water drain valve.
  2. After closing the valve, remove the hose from the cold water side and replace it with a cap.
  3. Remove the pump and the hose from the bucket, and then drain the liquid.
  4. Nex thing to do is to put the hose from the hot water drain part back into the bucket. To flush the heater with cold water, the next step will be turning on the cold water valve. Do this for 5 to 10 minutes.
  5. The next step will depend on if you have a condensing vs. non-condensing tankless water heater. Condensing units will have an additional drain opening on the very bottom of the unit. Open this up and place a bucket underneath to collect any excess water.
  6. You could also rinse the water filter to clean it out, but this is an additional step and is not necessary.
  7. Turn off the drain valve, remove the water drain hose, and then replace it with a drain cap.
  8. Lastly, turn on both hot and cold water valves again. Also, turn on the gas valve.
  9. For the units with a control screen, the error 11 will probably show again. All you need to do to remove it is to turn the unit off and then on again.

Tankless Water Heater Maintenance


 As previously mentioned, you should flush a tankless water heater at least once per year. This should be a part of a regular maintenance routine.

Also, this rule applies to any type of tankless heater you have. So, whether it’s a Rinnai or Noritz, or even Navien, this rule still applies.

We already explained how the hard water elements are actually what causes scale and other buildups inside a heater. You can postpone the flushing date by installing a water softener, which will clean out the elements present in hard water.

Some tankless water heaters even have alerts that notify you when there is a maintenance issue. If unsure, you can always contact a cleaning service to help you out on this task.


Tankless Water Heater Cleaning Service


Although descaling tankless water heater is a fairly simple task, most homeowners avoid doing it themselves.

There is a simple reason behind this, and it’s that you can end up voiding the warranty if you descale a tankless heater yourself.

To avoid situations like this, we recommend researching different water heater warranties. [4]

However, there are special cleaning services and licensed plumbers that are authorized to do this job.

Before we take a look at the maintenance costs, you may want to check our article on – Do plumbers fix boilers? 

Descaling Tankless Water Heater Costs

 If you expect a cleaning service to descale your tankless heater, it will cost you between $100 and $200.

However, there are other costs if you decide to do it yourself. First of all, we want to mention that buying a descaling kit is not necessary at all.

You may already have some of the supplies at your house, and other missing supplies can easily be borrowed. However, if you don’t, it’s probably best to save your time and invest in a descaler kit.

A descaling kit can cost you anywhere from $110 to $150. Purchasing a descaling solution separately will cost you about $50. A white vinegar bottle can be bought for $10-$20, so it’s not surprising it’s often being used in place of a descaler.

 The Takeaway

Descaling tankless water heater is an easy task, although it may seem tough at first glance.

The only thing that’s tricky about this process is that you need a specific set of supplies. These are sold in descaling kits, which contain everything you need for flushing your tankless heater.

By following the Step-By-Step in this article, your tankless will easily be cleaned of any scale. However, make sure that your product is not still under warranty because any DIY work can void the warranty.

You can also install a water softener to postpone the need to descale your tankless once every year.