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Need to Descale a Tankless Water Heater? Try this.

If you have hard water, you’ll need to descale a tankless water heater about once per year or even more depending on the hardness level.


While a tankless water heater is far less prone to limescale buildup than a tank-style water heater, you shouldn’t overlook its maintenance. Fortunately, you won’t need a plumber do put this method into practice. You can do it on your own, and it won’t take more than 90 minutes.


Many modern heaters have sensors and an alert system that tells you when there’s too much scale buildup. So if you have one of those, you won’t need to remember when was the last time you’ve descaled it. With that out of the way, here are the tools and items you’ll need and how to use them o descale a tankless water heater.


Tools and items that you’ll need


  • Four gallons of white vinegar
  • One tankless water heater descaling pump
  • Two ¾-inch drain hoses (or hoses the size of your heater’s connection)
  • One five-gallon bucket


You can buy everything except the wine vinegar as a single package called “tankless water heater cleaning kit.”


Many online stores and specialty shops alike should have these kits readily available. However, take note that you’ll probably spend more money on the package than if you were to purchase the items separately. It’s up to you to decide if you want more convenience or smaller spending.


Step by step guide on how to descale a tankless water heater


Once you get all these items, go through the descaling process as follows:


Turn off the heater


The first and most crucial step is to power off the heater entirely. If you have a gas heater, all you need to do is turn the gas valves counterclockwise.


For electric tankless water heaters, the process is a little trickier, but still doable on your own. Go to the breaker panel, find the circuit for the heater, and turn it off. Make sure also to turn off the heater itself. Doing so requires a little disassembly. Remove the cover plate and inspect every wire connected to the terminal with a contactless electrical tester. If the tester lights up, it means that the electricity hasn’t been completely consumed, and you’ll need to wait a while before working on the heater.


Warning: don’t try to descale the heater if there still are signs of electricity. Doing so will cause irreparable damage to the unit.


Turn off the water supply valves


Most water supply valves are located underneath the heater. Turn off both the cold and hot water supplies by rotating the valves counterclockwise. Also make sure to look for the service or draining valve because you will use it to flush the water that’s still inside.


Get an empty bucket and place it under the heater. To drain the unit, connect the hoses to the A and B valves of the isolation ports. You’ll get about one liter of water out of it. Once you’re sure the heater is empty, throw the water inside the bucket down the drain or the toilet.


Connect the hoses and descaling pump


Take one drain hose and attach one end to the blue cold water valve. Connect the other end to the submersible pump. Afterward, connect the second hose to the red hot water valve, and place the other end inside the bucket. Tighten the hoses with a wrench to make sure no leaks will occur.


Warning: make sure the pump isn’t plugged in the power supply just yet. Some pumps don’t have a switch, and they turn on automatically once you connect them to an electrical outlet.


descale a tankless water heater 


Add vinegar and start the process


Place the pump inside the bucket along with the other end of the hose that’s connected to the hot water valve. Pour four gallons of white vinegar over them and get ready to start the descaling process.


Now open the hot water valves and turn on the pump. Now let the pump run for about ideally an hour, or 30 minutes at the very minimum. Then turn off the pump and let the vinegar drain back into the bucket.


Clean the air intake filter


Until the heater flushes, you’ll have enough time to clean the air intake filter as well. Every model is different, so check the user manual to find out where yours is located and how you can access it.


Rinse the water heater


In the time it took you to clean the air intake filter, all of the vinegar should’ve flushed out already. Throw the vinegar away, and let’s start rinsing the heater.


Leave the hot water hose on and remove only the hose that’s attached to the cold water valve and the pump. Put the cap back on the service valve and turn on the cold water. The water will start flowing through your unit and drain back into the bucket. Once the bucket is full, turn off the water.


Turn your descaled tankless water heater back on


Disconnect the drain hose and reattach all the connections tightly. Now turn on the power and check to see if the hot water circulates as it should.


If there are no leaks and your unit works as usual, you’ve done everything right. On the other hand, if problems occur even if you’ve followed each step correctly, you might need to call an expert.


How does hard water affect the tankless water heater?


Hard water limits the effectiveness of appliances that use water, among which tankless heaters are included.


Even only a 1/50-inch scale buildup has the potential of decreasing heat transfer efficiency by 9.4%. As you can see, even little limescale buildup has a noticeable impact on the unit’s heating output.


Furthermore, this buildup has other devastating effects on the heater. It causes it to work harder and consume more electricity or gas than needed. In turn, the process reduces the heater’s lifespan by a large margin. Costly repairs will be due if you don’t solve the problem immediately.


How to avoid the need to descale a tankless water heater


The best way to prevent limescale buildup is to get a device that alters mineral crystals inside hard water.


A water descaler is perfect because it does so without adding sodium to your water supply, unlike water softeners.


The way a descaler works is simple and doesn’t require any plumbing skills whatsoever. Take the unit’s coils and wrap them around the main water pipe, as shown in the manual and installation video.


Then secure the coils in place with the provided zip ties and plug the unit into an electric socket. Once the light is on, the descaler emits electrical impulses through the coils, which produce a capacitive effect. Also called cathodic protection, this method relies on physics principles to protect metal against corrosion and hard mineral deposits.


The calcium and magnesium crystals become smaller and less sticky, so you still get the benefits of drinking hard water without its negative effects on hair, skin, and appliances.


What size tankless water heater do I need for my family?


Tankless water heaters bring numerous advantages compared to their tank-style counterparts. They offer an instant and seemingly endless flow of water while also consuming far less electricity.


Moving on, you also get the added benefit of lower maintenance and longer lifespan as well. Warranties are also usually higher, and some states even give you a tax break if you choose a tankless heater instead of a tank-style one.


And that’s not all. The most significant advantage a tankless heater brings is that it occupies less space. Still, you need to consider several factors depending on how many people your household has:


  • How big is the house?
  • What’s the water flow rate?
  • The rate at which temperature rises


The size of your house


A regular-sized house might only require a small tankless water heater. No matter if we’re talking about a gas or electric unit, 30 gallons are enough for one or two people who use it regularly. 40 or 50 gallons is recommended for one or two people that use it frequently.


For regular houses with two or three people, we recommend opting for a 40-gallon tankless heater if the usage is low. For high usage for the same amount of people, you should go for either a 50-gallon electric unit or a 40 to 50-gallon gas heater.


Moving on to houses with multiple floors and bathrooms, if three or four people live in such a place, you should go for a 50-gallon electric or a 40-gallon gas model on regular use. For high use, the difference is significant – an 80-gallon electric or 70-gallon gas tankless heater.


Finally, for villas with five or more people, you should consider purchasing an 80+ electric or 70+ gas tankless water heater. While there are no exact measurements to take into consideration, we hope our estimations will help you choose the right model.


Consider the water flow rate


When purchasing a tankless water heater, make sure to check out its GPM output. This is a crucial factor to consider if you have more than one bathroom and plan to use two showers simultaneously or if you want to take a shower and have your dishwasher or washing machine run a cycle at the same time.


To put things into perspective, let’s say one showerhead requires a flow rate of 1.8 GPM or efficiency. The other showerhead might require a different flow rate or a similar one. All you have to do is sum up the two showerheads’ flow rates to determine what GPM the heater should output.


For example, showerhead 1 (1.8 GPM) + showerhead 2 (2.0 GPM) = 3.8 GPM required output from the heater.


Temperature rise


You’ll also need to calculate the water temperature that flows in your home and the temperature you want your heater to produce.


Let’s say you want to take a 150° Fahrenheit shower, and the incoming temperature is 45° Fahrenheit. In that case, you will need a water heater with a 60° Fahrenheit capacity. Take note that groundwater temperature varies depending on the zone you’re in.


What is the downside of a tankless water heater?


We’ve already mentioned the good parts of a tankless water heater. Now let’s move on to its weaknesses to see if it is right for you or if you should consider replacing it with a tank-style heater.


It takes longer to deliver hot water


Even a completely descaled tankless water heater might take up to a minute to heat the oncoming water, whereas a tank-style model heats it almost instantly.


Inconsistent temperature when using multiple showers and appliances


Sometimes you might not be able to afford a tankless heater with enough GPM or temperature rise outputs to satisfy everyone’s needs.


In such cases, you might feel a significant drop in temperature when you’re showering if other people are also using water inside the household.


No power, no hot water


Even gas-powered tankless water heaters require electricity to activate the control panel and let the heater do its job.


So, in the case of a power outage, you’ll only get cold water no matter how long you wait. Until the electricity comes back on, there’s no way you can take a shower.


The bottom line


If you have or plan on purchasing a tankless water heater, you should consider getting a water descaler.


It will save you precious time and money that you would otherwise spend on flushing and maintenance. Even small scale buildup reduces its efficiency and life expectancy drastically, so a descaler is like a guarantee that your investment would have been worth it.


You can purchase our descaler from the link above or go Amazon to get it if that’s more convenient for you. The unit comes with a 10-year warranty as long as you opt to register the product on our website, regardless of where you purchased it from.