How to Clean a Tankless Water Heater

Part of our goal in building the Tankless Guide is to provide you with practical information you can use to get the most from your tankless heater. Tankless water heaters offer significant cost savings to homeowners as well as the wonderful opportunity to have on-demand hot water for as long as it is needed. They are also a great choice for homeowners pursuing a green lifestyle . To get the most from your investment from the model you choose, a tankless water heater annual cleaning is essential. Most manufacturers we cover in our tankless heater reviews  including Rinnai, Rheem, Navien  and others recommend regular maintenance as an important part of getting greater performance and longevity from your unit. When cleaned regularly as part of proper maintenance, a tankless water heater will last 2-3 times longer than a standard tank-style water heater — that’s 15-20 years of efficient water heating.

As a side note: We just noticed that we had all ready done an article on cleaning the tankless water heater earlier this year. It got buried in the archives of information. We hope that the duplication of this important task will serve as a reminder to all of readers that annual cleaning is very very important.

In this tankless water heater guide we look at how to clean a tankless water heater. The process is not hard to do and it will remove calcium deposits from the unit, keeping its efficiency and performance level as high as it needs to be. Heres how to clean a tankless water heater in 60-75 minutes.

Preparation Stage

Beforehand, gather the supplies that you’ll need. They include:

  • 3 garden hoses or washing machine hoses.
  • Pipe wrench.
  • 2 – 5 gallon pails.
  • 2 gallons of white vinegar.

In addition, before you touch the water heater, turn off the power supply to the unit at the circuit box and lock out the circuit if possible . Turn on a hot water tap near the heater and make sure that the unit does not turn on — verifying that the power is off.

Set Up the Equipment

What you are going to do to clean the tankless water heater is to circulate white vinegar through the unit with the utility pump. Knowing that may help you conceptualize what to do.

1. Shut both hot and cold water valves on the pipes leading to the water heater.

2. With a bucket beneath the unit, open the drain caps and let the unit drain. Once it is empty, make sure the rubber washers are still in place. If not, check in the bucket. Empty the bucket.

3. Connect one hose from the cold water inlet on the heater to the outlet side of the pump.

4. Connect a second hose to the inlet side of the pump and let the loose end rest in the first bucket.

5. Attach the third hose to the hot water inlet on the tank and let is rest in the second bucket.

Now you’ve got everything in place.

Cleaning your Tankless Water Heater

Pour the white vinegar into first bucket, the one with the hose attached to the inlet side of the pump. Plug in the pump — and turn it on if it has a separate on/off switch. The pump will pick up vinegar and pump it into your tankless water heater. It will cycle through the heater and empty through the hose laying in the second bucket.

After a few minutes of cycling, you might notice that the vinegar begins to turn cloudy. That is evidence that the calcium and other minerals built-up in the heater are being dissolved. When the first bucket is nearly empty of vinegar, turn off the pump. At this point, you can pour all the vinegar into one bucket and put both loose ends of the hoses in it. Turn the pump back on and let the vinegar cycle for 40-60 minutes

As a side note: We recommend that you follow the above procedure and after you have become confident with how easy it is to do the cleaning yourself  then if you wish to reduce the number of steps involved in setting up the cleaning. You can use only one five gallon bucket as shown in this  great annual tankless water heater cleaning video.


This is the best way to clean your tankless heater whether it is a single point or multi point heater . A tankless water heater annual cleaning is an affordable way to extend its life and keep it running efficiently. For more answers to cleaning your tankless heater check out Rinnais FAQ page.


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