Informational Guide

How To Descale A Tankless Water Heater

by Andrew

Tankless water heaters are convenient because they require little maintenance; however, it is necessary to descale tankless water heaters. We walk you through step-by-step how to descale your tankless water heater at home by yourself or with the help of a professional.  

You need to descale a tankless water heater because minerals exist in the water that we use in our home. If you have hard water, you will have more minerals and a thicker scale build-up.

However, regardless of the type of water in your home, you will need to remove the organic and inorganic deposits that build up in your tankless water heater over time. 

The benefits to the homeowner when descaling is that your water will stay warm continuously, your tankless water heater will last longer, and the water flow will not be constricted due to mineral deposits. 

outdoor tankless water heater

If you do not descale your system, the deposits can inhibit the flow of water and also keep the heat exchanger from working correctly, which means that your water won't stay at an even warm temperature when you need it.  

How To Descale Tankless Water Heater (DIY Step By Step Guide) 

Our step-by-step guide on how to descale a water heater will walk you through the process. You can hire a professional to perform this service for you, but it isn’t difficult to do on your own at home.  

  1. 1
    To begin, gather your supplies: descaling solution or vinegar solution, five gallon bucket, stainless steel washing machine hoses, and tankless water heater descaling pump. These items can be purchased separately or as part of a tankless water heater cleaning kit that you can find in local stores like Home Depot or online on Amazon. 
  2. 2
    Next, it is crucial to shut off the water to your tankless water heater. We recommend pulling out the manufacturer manual for this part to ensure that you turn off all access to the water. You also need to turn off the gas access to your water heater. Once you have turned off both the water and gas, you can unplug the water heater from the wall outlet. 
  3. 3
    An external pump holds water and will release water once turned off. This is where you should place your bucket to catch any water that does fall. Slowly begin to unscrew the service valve for the cold water side and the hot water side. 
  4. 4
    Now it is time to throw away the wastewater and use the bucket to fill up with your descaling cleaning solution or vinegar. 
  5. 5
    Then attach your hose to the pump and place the pump into the bucket. Turn on the tankless water heater and let the pump move the solution through the cold water valve and out the hot water valve, and then into the bucket. Let this run for approximately 45 to 60 minutes. 

If you prefer to use a home solution, descaling tankless water heater with vinegar is an option. This option works best if you use it more often. If you planned to descale your tankless water heater every year, we recommend doing so every six months if you will be using vinegar rather than a descaling solution. Vinegar tends to be gentler on the deposits and may not soften the most arduous deposits if you wait too long in between services. We recommend purchasing white vinegar. You can find white vinegar at the grocery store. You will need approximately 4-5 gallons to descale your system.  

  1. 6
    This is also an excellent time to clean out the air intake filter. The descaling filter for tankless water heater is actually the air intake filter, but it helps to keep deposits out by keeping the system clean. 
  2. 7
    This is also an excellent time to clean out the air intake filter. The descaling filter for tankless water heater is actually the air intake filter, but it helps to keep deposits out by keeping the system clean. 

Water Heater Descaling Solutions – Which Is Best? 

A tankless water heater descaling solution works by dissolving the mineral build-up and rust on your heat exchanger in the tankless water heater.

The solution dissolves the deposits and then is washed away through the drain. 

A descaling solution can also be used in other home appliances such as ice machines, humidifiers, boilers, chillers, and water lines. The descaling solution is a key piece of descaling your water heater.  

Vinegar is also an at-home descaling solution option, but we recommend using a descaling kit for your annual or every 3 years descaling. 

tankless water heater

If you plan to flush your tankless water heater more often, a vinegar solution will suffice, but for the routine option, it’s best to use a descaler solution. The Home Depot tankless water heater descaler is our favorite because it is affordable, quickly dissolves inorganic deposits, and washes away easily.  

How Often Should You Descale Tankless Water Heater? 

You should descale your tankless water heater every 1-3 years, depending on the brand and type of tankless water heater. When you descale your tankless water heater, you remove all of the scale build-ups that have taken place throughout using the appliance. Hard water has more minerals than soft water, so if you live in a hard water area, your system will automatically attract limescale and mineral deposits. You can test your water to find out what hardness level your water is currently at, and if it is at a 5+ (on a scale of 1-10 typically), then you will need to descale your water heater every year. If you have a water softener installed or if you have softer water naturally 1-4 (on a 1-10 scale), then you can wait and descale every 3 years.  

There are a few signs that show you when you need to descale your tankless water heater. Water heaters begin to make noise when they need to be descaled because the build-up becomes too thick and creates weird noises. Another sign is that your hot water bill goes up. When there is too much scale build-up in the machine, it costs more to heat the water. You may also not get enough hot water no matter how long you let the water run, as limescale will prevent the heat transfer from moving smoothly. These signs do not always occur, and you won't know when to descale. This is why it’s important to descale your tankless water heater every 1-3 years regardless of signs.  

Descaling Popular Tankless Water Heater Brands 

Navien offers tankless water heaters as well as condensing boilers. We recommend flushing their tankless water heater models every two years with soft water and one year with hard water. 

The Nortiz brand is an expensive option but perfect for commercial use. If your home doubles as your place of business, you may want to consider a Noritz model. These tankless water heaters should be flushed every year. 


Rheem is a premier manufacturer and offers high-end tankless water heater models. We recommend flushing these models yearly to make sure that you keep this more expensive model in pristine condition. 

The Rinnai line tends to make simple and economy-focused models, which are easier to descale at home. Refer to your instruction manual for the best results. 

outdoor tankless water heater

Bosch is a premier manufacturer and recommends flushing their line of tankless water heaters once per year. Bosch is one of the more pricy tankless water heater manufacturers. 

Takagi has a wide range of tankless water heaters and is manufactured in Japan. We recommend the T-H2 model for most homeowners who want a solid gas tankless water heater model. 

How To Prevent Scale Build Up In Your Tankless Water Heater 

One of the best ways that you can help your water heater last for years to come and make the descaling maintenance process more straightforward is to prevent scale build-up in your tankless water heater. The better you prevent scale build-up, the easier the tankless water heater will be to descale.  

An effective way to prevent scale build-up in a tankless water heater is to install a water softener. The reason why scale build-up occurs is due to hard minerals binding to the tank when cold water becomes hot. If you remove those minerals from the water, there won’t be anything left to create excess scale. The benefits of water softeners do not stop at preventing scale build-up either. Water softeners also lead to smoother skin, softer hair, and make it easier to clean your home (more suds and more killing bacteria strength thanks to the soft water).  

Another effective preventative measure is to use vinegar or lye during each flush. These organic chemicals are best used with calcium build-up specifically. You can flush the water heater, add these chemicals (choose one), and then flush the water heater once more. This is an option for people who do not want to do a full descaling but want to keep their tankless water heater clean with multiple flush-outs throughout the year. It’s not necessary, but if you have the time, it can prevent scale build-up and make the descaling process simpler.  

People Also Ask (FAQs)  

How much does it cost to descale your tankless water heater? 

It costs approximately $120 to $180 to descale a tankless water heater. It is recommended that you descale your tankless water heater every 1-3 years. If you have well water, then the recommendation is every year due to the additional levels of minerals in your water.  

How long does descaling a tankless water heater take? 

It takes approximately 45 minutes to descale a tankless water heater. You can perform this on your own if you have a tankless water heater model that is easy to use. You can also hire a professional to descale your tankless water heater for you.  

What happens if you don't descale your tankless water heater? 

If you do not descale your tankless water heater, then you risk a build-up of sediment, which can damage the heat exchanger. If you damage the heat exchanger, your tankless water heater will fail to heat your water. When this happens, you have to replace the heat exchanger or purchase a new tankless water heater. If you plan to use your water heater for years to come, then you need to descale it regularly.  


Tankless water heaters are convenient home appliances that can be used to save money and give you access to unlimited hot water. Every 1-3 years, you will need to descale your tankless water heater in order to keep the appliance running smoothly. Remember to follow the preventative tips to make the descaling process easier and keep scale build-up at a minimum.