How To Flush a Tankless Water Heater The Easy Way

Last Updated On July 14, 2024

Updated on March 31, 2023



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how to flush tankless water heater

Knowing how to flush a tankless water heater will save you a fortune in years to come. 

Most tankless unit warranties won’t cover damage from lime deposits, so the tankless water heater maintenance falls on you as the homeowner. It needs to be cleaned out once a year.  

Lime and calcium start to build up in the tankless unit, and will affect the heating element and the valves. 

Breaking down this hard water scale and flushing out the sediment is crucial, and prevents expensive plumbing repairs. 

We’ll show you the easy way to do tackle this without calling for plumbing service!

What's In This Guide?

      How to Flush a Tankless Water Heater: Quick Tips

      If buildup isn’t too bad, white vinegar can work as a cheap solution the next time you flush the tankless hot water heater.

      You can also buy this handy kit with everything you need, including the cleaning solution! (More on that later.)

      Here is a great video showing you how to flush a tankless water heater the easy way. 

      Now, here is your list list for how to flush a tankless water heater in five easy steps. This works no matter what type you may have in our home.

      Pro tip: You can buy a tankless water heater flush kit for half the cost of a professional plumber. You can use vinegar as a substitute for the cleaning solution when you reuse the kit. 

      You can do this without it, but this is much easier with a kit. We review the best kits, here.

      5 Steps to Flush Gas or Electric Tankless Hot Water Heaters:

      Step 1: Turn shut-off valve off. The first thing you need to do before flushing you tankless water heater is to shut off all the incoming lines. You need to shut off the incoming cold water and the outgoing hot water valves. 

      You need to turn the shut-off for the gas into the off position if you have a gas tankless water heater. 

      Before Flushing Tankless Gas Units: One way to tell if a valve is on is if the handle to the shut-off valve runs parallel to the pipe. You need to be sure that the valve handle is perpendicular to its corresponding plumbing pipe. 

      Before Flushing Tankless Electric Units: You can simply unplug the tankless water heater if it is electric. The tankless water heater is isolated now that all incoming water, gas, and electricity are disconnected.

      Step 2: Unscrew the service valves and drain. There are two ports between the water lines and the tankless water heater unit. These are service valves that allow us to drain the system.

      Water will flow freely from the service flush valve as soon as you unscrew the purge port valve cap. You can use the hoses and the bucket provided in the flush kit to prevent from making a mess and flooding our work area. (You could also use a garden hose if you have the right attachment.)

      You won’t see more than a trickle out of the cold side. The hot water side of the system will pool more and can still be hot. Be careful. You’ll need to be quick with the hose when unscrewing the cap to divert the water and not burn yourself.

      Step 3: Pump with cleaning solution or vinegar. You can now screw on the two hoses that came with the flush kit if you didn’t during the draining process. 

      You’ll need to connect one of these hoses to the sump pump. The other hose will be used for drainage. 

      Connect the cold side of the tankless water heater to the submersible pump. The hot side of the unit will be to drain the sediment and build-up. 

      You can turn on the pump and flush the system for about an hour. A 4-gallon container of food-grade vinegar costs less than $20 And works well on the lime and scale.

      Step 4: Replace the air intake filter. Every tankless water heater has an air intake filter. The location of this filter can vary depending on the brand of a tankless water heater. The filter may not be conspicuous. You will most likely need to remove a panel or cover to get to it. 

      This filter is a lot like changing an oil filter when replacing our car’s oil. You want to do everything you can to extend the longevity of our tankless water heaters life in addition to regular flushing. 

      Changing out the air intake filter is an important step. You must change this filter every time you flush our tankless water heater.

      Step 5: Rinse out the system. You’ll need to rinse the tankless heater after you flush it with the cleaning solution or vinegar. Both products are non-toxic, however, the smell can be pretty awful. 

      You can reuse the same buckets that you used to flush the system to rinse it. You can fill the buckets with water instead of white vinegar. Drop the sump pump into the bucket of water. 

      After you connect the hose from the pump to the cold water supply valve of the water heater, you’ll allow the pump to run for about an hour. You have now flushed the hot water heater and rinsed it out.

      That is how to flush a tankless water heater!

      You can turn all the water valves back to the “on” position.  

      It is safe to return the electric or gas to the hot water heater at this point, as long as you know there are no leaks. 

      did you know how to flush tankless water heater

      What Supplies Do I Need to Flush a Tankless Water Heater? 

      Buying a tankless water heater flush kit is the cheapest way to flush a tankless water heater. 

      As we said, this kit comes with everything, including the cleaning solution. 

      You can buy all the tools you need individually if a kit isn’t available. 

      Luckily, you can pick up everything you need at the hardware store. The following list is everything you will need to flush a tankless water heater.

      1. A 5-gallon bucket
      2. 2 stainless steel washing machine hoses
      3. A small submersible pump 
      4. 4 gallons of food-grade vinegar. (You may need to buy this at the grocery store.) 

      What is the Cost to Flush a Tankless Water Heater?

      It can cost over $200 to have a professional plumber flush your tankless water heater. You can save a fortune by purchasing a tankless water heater flush kit for around $125, and reusing it every year.

      You will only need to buy 4 gallons of vinegar when you want to flush your tankless water heater once you own the kit. 

      The flush kits for a tankless water heater come with everything you’ll need, including the cleaning solution. It also comes with a small bucket, a submersible pump,  and two small hoses. 

      You can buy all these items separately, but the kits help guarantee that you’ll have what you need.

      It’s nice having everything in one package rather than taking multiple trips to the hardware store.  

      How Do You Flush a Rinnai Tankless Water Heater?

      We see this question a lot, but you often don’t need brand specific instructions. 

      Hiring a professional plumber to flush a Rinnai tankless water heater can be extremely expensive. The cost shoots way up when you call them yearly for routine maintenance. 

      If you’re wondering, “how do you flush a Rinnai tankless water heater?” Using the five steps above will work for you too!

      Flushing a Rinnai tankless water is as easy as turning off the necessary shut-offs and unscrewing the isolation valves. Next, flush the Rinnai tankless water heater with a cleaning solution or vinegar and give it a good rinse. 

      Don’t forget to change out the air filter. You can now plug the Rinnai tankless water heater back into the wall. You can feel comfortable Flushing your tankless water heater now, no matter what type you have

      Tankless Water Heater Flush FAQs 

      How often do I flush a tankless water heater?

      You should flush your tankless water heater every 12 to 18 months. This can vary depending on the hardness of the water.

      Can you flush a tankless water heater with vinegar? 

       It is perfectly safe to flush a tankless water heater with vinegar.  In many cases using vinegar can save a fortune in common tankless water heater problems.

      How much does it cost to flush a tankless water heater? 

      It can cost over $200 to hire a professional to flush a tankless water heater. A flush kit costs on average $125. Once you have the flush kit you can buy a $20 bottle of vinegar each time you 

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      About Plumbing Navigator

      We write about "all things plumbing," helping you navigate common questions, repairs, and the best plumbing products on the market.

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      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

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