How To Flush Your Tankless Water Heater?

Tankless water heaters help to get hot endless hot water for showers. They also last much longer than a standard storage tank water heater. But for that they need to be maintained properly. Did you know it is important to flush tankless water heater at least once a year to prevent damage from calcium and mineral deposits. If the water is hard, then you will need to flush it more often.

Why do I need to do this?

Too much of calcium and mineral deposits can reduce the life of the tankless water heater. Regular flushing is quite beneficial for its longevity and improve its efficiency. It will also take longer for the water to get hot which will increase energy costs too.

What is needed for flushing my tankless water heater?

  • 4 gallons of white food grade
  • vinegar
  • 2 hoses
  • A submersible pump
  • A 5 gallons bucket

Where do I start?

Please go through the instruction manual that you got with the tankless water heater thoroughly before you begin. The first important thing that you should do before starting the flushing process is to switch off the gas connection.


Close the water valves. One colored blue brings cold water to the tankless water heater while the red colored one bring outs the hot water.


Open the 2 valves that are fitted for flushing. When you open them , the water that is already present in the water heater will come out. It is important to be very careful as the water that flows out may be hot. Doing this a few hours after the tankless water heater has been used would be the best. You should slowly open them and let all the water flow out. If there is a lot of sediment inside, the water that come out may be quite unclean. Then you may need to fill up the tank and empty it repeatedly till the water does not have any loose sediment. You can skip this step if you may wish to. But doing this may improve the impact of the flushing in removing the calcium and mineral deposits.


While the water empties out of the tankless water heater, pour 4 gallons of vinegar into the 5 gallon bucket. Take the 2 hose pipes and attach one end to each of the valve. The other end of pipe connected to the cold water line should be attached to the pump so that the vinegar can move around the tankless water heater. The other end of the other pipe should be placed inside the bucket so that the vinegar can come back into the bucket which will complete the process. Ensure that all the pipes are secured properly and will not cause any spilling of vinegar.


Insert the submersible pump into the bucket and plug it in. These pumps normally do not have any on/off button so this should ideally be the last step that you should do before you begin flushing the tankless water heater. Ensure that everything is kept on a smooth, even and steady surface to prevent any overflow of vinegar. Let the pump run for a hour to an hour and half.


Once the flushing is complete, dispose off the used vinegar, preferably into the drain. If you wish to remove the taste and smell of vinegar, you could use just clean water to just wash the insides again for several minutes. Just fill the bucket again with clean water and run the pump again. Another way could be to simply remove the pipe from the cold water valve and close it. After that just open the lever that brings in the cold water. The water will come out of the hot water valve after moving through the whole tankless water heater. You should keep the bucket to collect the water.


Remove the hose pipes and close both the flushing valves. Open the water valves and switch on the gas or electricity. Open the taps or the shower to check if the tankless water heater is functioning properly or not.

Use a wrench if necessary. But you should also be careful that you do not damage anything. Once you understand the process of flushing the water heater, it will become quite easy.

You could go through this video to understand the process of flushing a tankless water heater much better, if you are still unsure or doing it for the first time.
  1. I'm grateful for you helping me to understand that it is important to flush the water heater in your home so that mineral deposits do not build up inside of it. I'm not a very handy person, so I'm afraid if I attempted this by myself I might break something. It would probably be best if I hired a professional to flush my heater for me.

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