How To Flush A Tankless Water Heater? Step by Step Complete Guide 2021

Are you looking for an in-depth guide on “how to flush a tankless water heater” because debris and calcium have accumulated on the heating elements and inside your unit’s filters? If so, you have come to the right place.

Your machine provides you with perfectly hot water on demand whenever you need it. The times you realize it’s worth can often be when it suddenly stops working or is backed up.

To ensure it is functioning appropriately, you have to flush it on a regular basis to keep it running at its best capacity.

If you won’t flush it, you will have to pay unnecessary fuel payments and your device’s life will also be decreased.

Though, we recommend hiring a professional maintenance service for your heater annually. However, cleaning a tankless unit is very easy, so you can also flush it yourself to save money. 

This detailed guide will show you “how to flush a water heater with bleach”.

But, first, we will look at why flushing a heater is important and how often you should flush it. So, let’s get started.

Why It Is Crucial To Flush The Water Heater?

With prolonged usage, they start to store calcium and sediment buildup that is naturally present in the water supply.

When sediment accumulates and clomps together, it causes incompetence and damage to the device.

Therefore, you should clean it to prevent increased sediment accumulation and ensure that it works efficiently.

If you are experiencing some issues such as temperature problems, noisy heater, smelly water, etc. with your unit, you can resolve them with a simple flush.

How Often Should You Flush Your Unit?

How To Flush A Tankless Water Heater

It heats water on demand and does not deposit water in the boiler.

The manufacturers recommend flushing a unit annually to get rid of calcium and sediment buildup inside the appliance.

If you live in an area with hard water, you may need to flush it twice a year.

Regular flushing can help you extend its lifespan and ensure the best performance.

How Much Does It Cost To Flush A Water Heater?

If you want to do it yourself, it won’t be costly at all. The equipment required to flush it can be found at the house apart from the pump.

However, if you don’t have the items at home, you may have to spend $100 to $150 to buy them. If you want to hire an expert, you will definitely have to pay more.

How To Prepare For A Flush?

Isolation Valves

They are utilized for isolating a heater from the service. They come with a water pressure relief valve.

The red and blue knobs are used for opening and closing the cold and warm water service ports, whereas the yellow knobs are utilized for shutting off the cold and hot water.

They are available in various shapes, but they have two types: rotary movement and linear. Isolation valves are optional.

Some water heater companies offer isolation valves with their machines, while others leave the choice on the technician or homeowner.

If your heater does not have these valves, you should get them installed and also hire a plumber to flush your tankless unit for the first time.

Flush Kit And Pumps

Kelaro Tankless Water Heater Flushing Kit - Just add Vinegar Descaler

You also need a high-quality submersible pump and a big bucket while preparing for “how to flush a tankless water heater”.

If you want, you can use a flush kit. These kits are easily available in the market and include everything you need such as a pump, a bucket, hoses, etc.

It is not necessary to have a kit, but it can make the flushing easier for the first-time heater owners.

Things You Will Need To Flush A Tankless Water Heater

  • Screwdriver
  • Adjustable wrench
  • Needle nose pliers
  • 5-gallon bucket
  • Non-contact electrical tester
  • Pond pump or small sump pump
  • 6-foot long washing machine hoses with connectors
  • 4 to 5 gallons of white vinegar

How To Flush A Tankless Water Heater Gas?

How To Flush A Tankless Water Heater Gas

Before flushing a gas heater, make sure to read the user manual because it has particular guidelines to flush and descale the unit.

It does not matter which brand’s gas unit you have, there are some stages in cleaning that must be completed in order.


  • Cut off the electrical power going to the water heating machine.
  • Take out the access panel and use a non-contact voltage tester to examine the wires going into the terminal to confirm that no electricity is reaching the appliance.
  • Now, turn off the hot and cold water valves to prevent cold water from entering the device and plumbing system.
  • Then, find the warm water pressure relief valve on the hot water line and open it to relieve the pressure. While doing this, be cautious because the water can be extremely hot.
  • Now, locate the hot water service port and cold water service port. You have to attach hoses to both of them.
  • Put the pond pump or small sump pump into the 5-gallon bucket and connect the cold water hose to the pump.
  • Put the other end of the hose into the bucket. 
  • Add 4 gallons of virgin, food-grade, and white vinegar into the bucket, but don’t dilute the vinegar.

How To Flush A Water Heater Gas?

  • The next step of “how to flush a water heater with vinegar” is to open the cold and hot water service ports.
  • Activate the pump. The vinegar should flow through the heater for at least one hour to break down the scale and flush out the sediment from the machine.
  • Make sure the pump runs at a rate of four gallons in 60 seconds. If it flows at a slow rate, allow the vinegar to flow through the unit longer.
  • Shut the pump off and dispose of the vinegar.
  • Close the cold water service port. Take out the connected hose.
  • Open the cold water shut-off valve but don’t open the hot water shut-off valve.
  • With the cold water shut-off valve, fresh water will start to circulate through the heater and flush out any residual vinegar through the second hose into the bucket. The fresh water should flow through the heater for a minimum of ten minutes.
  • Close the cold water shut-off valve to stop the water from circulating through the device.
  • When the water finishes draining, eliminate the second hose and close the hot water service port.  


  • Change the filters and open the cold water shut-off valve and hot water shut-off valve.
  • Change the access panel and open the gas shut-off valve.
  • The last step of “how to flush a tankless water heater” is to restore the electrical power.

How To Flush A Hot Water Heater Electric?

How To Flush A Hot Water Heater Electric

Flushing an electric device is somewhat different from gas heaters and you may have to disassemble some of them.

Navien water heaters are very straightforward, but Takagi machines are a little bit difficult to flush and require additional steps to place the water control valve correctly.


  • Disconnect the electrical power to the appliance at the circuit breaker.
  • Close the cold water shut-off valve. It will prevent the water from entering into the unit.
  • Open a tap to permit the water to drain from the machine and close the hot water shut-off valve.
  • Take out the access panel and use a non-contact tester to ensure the electricity is not leading to the unit.
  • Eliminate the wires connected to the heating elements’ top by loosening the screws.
  • Rotate the heating element’s hexagon brass top in a counterclockwise direction to remove the heating element from the copper tank.
  • Examine the heating elements for any sort of damage. If you notice any damages, replace the heating element immediately.
  • Put the heating elements in the unit’s copper chambers.

How To Flush A Water Heater Tank?

  • After placing the heating elements inside the chambers, fill them with food-grade, vinegar, and diluted virgin.
  • Let the vinegar stay in the chambers for 90 to 120 minutes.
  • Drain the vinegar. Change the heating elements and re-attach the wires to the top of the heating elements.
  • Now, open the cold water shut-off valve and fill the tank with water.
  • Inspect the tank for leaks while it is filling. Then, open the hot water shut-off valve and several hot water fixtures. Let the water flow through the fixtures for five minutes to flush out the vinegar and remove air pockets in the pipes.


  • Deactivate all hot water faucets and close the cold water shut-off valve.
  • Take out the cold water inlet filter and clean it with cold water to get rid of any debris.
  • Replace the cold water inlet filter back on the cold water line.
  • Close the access panel and re-connect electrical power at the circuit breaker.



With regular maintenance, your unit can have a life of more than 25 years and you can save a lot of money in utility costs.
If you are a new tankless device owner, you should consider employing expert services to clean your machine the first time.
Obviously, you will have to spend money, but you will have mental peace because you will know that a professional will perform his job in the right manner.
However, if you want to “how to flush a water heater yourself”, then follow the instructions given in this article.

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