Descaling a Tankless Water Heater and Maintenance Tips

plumber with pliers and water clock

Descaling a Tankless Water Heater and Maintenance Tips

A lot of people wonder if they need to do maintenance on their tankless water heater, and if so, how hard it is to descale a tankless water heater.

Luckily, you may not need to service your tankless water heater at all (we’ll explain below). But even if you do end up needing to service a tankless water heater, you will see that it is not difficult to do.

In this article, I will give a detailed guide on how to descale a tankless water heater yourself, when you need to hire a technician and how to keep your on demand heater working for decades.

How Do I Know If I Need to Descale a Tankless Water Heater?

If you live in an area that is known for hard water, you should regularly descale your tankless water heater.

This map from the USGS website shows you the areas of the country with hard water and how high a threat it would be to your tankless water heater. If your area is highlighted white or red then you definitely will need to do a routine flush to rid your tankless of scaling buildup.

Courtesy of USGS

Other areas in blue probably won’t need any flushing but you may decide to stay on the safe side and do it every couple of years or so.

If you still aren’t sure, don’t worry, most modern water heaters will have either an app that sends service alerts to your phone, or error codes on the LED that alert you to some maintenance issue. If you have a smart tankless, then it runs its own diagnostics and can tell you the specific problem.

When you get an alert that your tankless water heater is not firing properly or that there is a pressure problem, then it definitely is the time to have a plumber come out to your house.

How to Descale your Tankless Water Heater

This sounds serious but servicing the tankless water heater yourself is not much work.

Here are the materials you need to start descaling your water heater:

  • Submersible pump
  • Rubber hoses to attach to the valves
  • 5 gallon water collecting bucket
  • Vinegar or tankless water heater descaling solution

You can get all the needed materials with a good descaling kit, like this one.

Descaling Kit
126 Reviews
Descaling Kit
  • 6 Piece Tank-less Water Heater Flush Kit. Helps maintain and extend the...
  • Works with most all tankless water heaters such as Rinnai, Bosch, Noritz,...
  • Our cleaning solution removes scale deposits from tankless water heaters,...
  • 6 Foot hoses easily connect to tankless heater valves, and the kit will...
  • ChromeX manufactures thoughtful tools and accessories for both the...

Here are the steps on how to descale a tankless water heater

  1. Set temperature to 150F and let water run for a minute.
  2. Shut off all power to water heater.
  3. Close income and outgoing water isolation valves.
  4. Get your bucket ready to collect about a liter of draining water.
  5. Drain unit and connect hoses to the drain ports of isolation valves “A” and “B”
  6. Prepare bucket that contains solution to be pumped through the heater.
  7. Fill bucket with descaling solution and water.
  8. Open isolation valves “A” and “B”
  9. Turn on circulation pump and let solution circulate for 30-60 minutes.
  10. Drain descaling solution from heater and flush water through heater by closing valve “B”.
  11. Open up valve “A”with a hose leading to an empty bucket.
  12. Open up inlet water valve to let fresh water through and empty solution out into bucket.

That’s it as far as how to descale a tankless water heater goes. This should only take 5 minutes of time and does not require a professional.

If you are unsure of your ability to do this, just watch this quick video on how to descale a tankless water heater and you will see that it does not take a pro to do this.

Flow Aide vs Vinegar

Which solution works best is kind of not up for debate. The Flow Aide works a lot better than vinegar. Especially if there is a lot of build up.

If you haven’t flushed your tankless water heater in a few years and you live in a hard water area, then I would definitely go with the Flow Aide.

Though vinegar doesn’t work quite as well, it does work. So, if you are doing a regular flushing once a year, then you can probably use vinegar and see good results.

Basically, it comes down to how much is it worth to you do ensure that the lime is really gone.

You can check the price here on Amazon for a gallon of Flow Aide, and you see that it isn’t exactly cheap. With that gallon, you should get 3 or 4 flushes, however.

Vinegar is obviously much cheaper, so even if you have to descale more often when you use it, you are saving money.

As with most things it comes down to your money or your time. I, for one, would rather spend a few more dollars to wipe out any lime and not worry about how effective it was so I can save myself some time later.

Not only that, but the Flow Aide is odorless and the vinegar can make a big stink when you are doing the flush.

Read This Next

There are a few tankless flushing kits out there that make it super easy to keep your tankless running smoothly for a really long time. Click that link to read the reviews.

Tankless Water Heater Maintenance Costs

If you are thinking of getting a professional to flush out your tankless water heater periodically, that can be expensive.

Since rates vary wildly, I can’t put an exact number on it, but expect to pay between $100 and $200 to service your tankless.

This should include the descaling, cleaning of the filter and possibly replacing it, and doing any diagnostics of the tankless water heater system to make sure it is running properly.

If all you are worried about it descaling, then you can do it yourself for a fraction of that cost and it only takes an hour of your time.

Get yourself a pump flush kit descaler and it will pay for itself.

How Much Does a Tankless Water Heater Flush Kit Cost?

A decent flush kit shouldn’t cost more than $150.

A descaler kit will come with a tankless water heater descaling pump and hoses that attach directly to the isolation valves or water inlet.

An excellent one that I recommend is Chromex Descaler Kit. It has the pump, hoses, 5 gallon bucket and descaling solution.

Chromex Tankless Water Heater Flush Kit with Certified Liquid Descaling Solution and 1/6HP Extra Strength Pump
126 Reviews
Chromex Tankless Water Heater Flush Kit with Certified Liquid Descaling Solution and 1/6HP Extra Strength Pump
  • 6 Piece Tank-less Water Heater Flush Kit. Helps maintain and extend the...
  • Works with most all tankless water heaters such as Rinnai, Bosch, Noritz,...
  • Our cleaning solution removes scale deposits from tankless water heaters,...
  • 6 Foot hoses easily connect to tankless heater valves, and the kit will...
  • ChromeX manufactures thoughtful tools and accessories for both the...

Let’s say you buy the descaler kit above. You just paid for the cost of a professional and it can be used for years. It paid for itself after the first use.

Now you only need to get the descaling solution, which costs about $20. I would say that that works out to being pretty cheap and only costs you less than an hour of your time.

How Often to Descale your Tankless Water Heater

Whether or not you ever need to descale your tankless water heater will depend on a few things.

As I mentioned, you may not even need to do anything besides a few routine checks occasionally.

The number one reason you may need to service tankless water heaters is because of scaling caused by hard water. This video provides an excellent primer on hard water and the problems it causes.

If you have hard water and have your inline water heater set to a very hot temperature, then you may need to flush it once a year.

Flushing it with a solution or vinegar will descale, or delime your heat exchanger and keep it running efficiently.

Even if you do live in a hard water area, you still may not even need to do it that often.

Some units will send you an alert if your tankless water heater needs descaling. If you really want more details about hard water affects a tankless water heater then definitely read this detailed article I wrote about it by clicking here.

If you live in an area with hard water and just want to be sure that your tankless water heater is running efficiently and doesn’t have any lime build up, then go ahead and flush it every year.

Otherwise, if you don’t live in an area with hard water, check your error codes periodically and flush it when it indicates it needs servicing.

For peace of mind, go ahead and flush it out every couple of years just to be on the safe side, but understand it probably isn’t necessary.

FAQ about Descaling Tankless Water Heaters

Do Electric Tankless Water Heaters Need to Be Flushed?

Yes they need to be flushed. Lime scale builds up on the heat exchanger of an electric tankless water heater just as easily as it can on a gas.

There are plenty of differences between a gas and electric tankless water heater so if you haven’t decided which one to buy just yet then I recommend checking out that article.

How do I flush a Rheem tankless water heater?

Rheem tankless water heater descaling follows the same process as other water waters. This short video explains the process.

What happens if you don’t flush your tankless water heater?

Maintenance of a tankless water heater including descaling is very important if you suspect it has lime build up. The scale build-up erodes your tankless water heater over time, which will cause big issues if left unserviced.

Even a thin layer of scale will increase your energy costs by up to 30%. This essentially negates any of the savings of using a tankless vs tank system.The heat exchanger strains to produce hot water and this limits the lifespan of your water heater.

Final Thoughts on Tankless Water Heater Descaling

If you are reading this before you bought your tankless water heater and want to know what you are getting into as far as descaling and maintenance, don’t worry. It really is not that bad.

And in my mind it beats having to worry about a flooded basement with a leaking storage tank water heater system. Or going a long time with cold water.

Most tankless water heaters have the isolation valves already installed or at least come with the kit so you can add them if you want. These will really make maintenance a lot easier.

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