How to Flush a Tankless Water Heater?

Tankless water heaters are popular among homeowners and many other users. This is because of their ability to continuously supply hot water on demand. Remarkably, they are environment-friendly.  But, do you know how to flush a tankless water heater? It is imperative to do this regularly. I personally prefer doing this twice a year.

However, if you check your model manual, the chances are that you will come across a recommendation to flush your tank annually. This is because the tank’s functionality and design require maintenance to function efficiently and effectively with time.  In the long run, you increase its durability.

Flushing your tank helps save significant amounts of energy as opposed to traditional tankless water heaters. Gratefully, this review helps you understand how to flush a tankless water heater to remove mineral build up in the unit, clean up the screen filter, plus much more.

Flushing a Tankless Water Heater

Most folks would like to attach a hose to the tank using vinegar to do the flushing. However, whichever approach you prefer, it is imperative to clean thoroughly the air filter.

Whether you are a newbie into tankless water heaters, DIYer, or a de-scale novice in the industry, the whole exercise doesn’t have to be energy-draining. In most cases, you will need a maximum of an hour, and your tankless water heater is ready for use. These steps will help you flush not only your tank but also save your precious time.

Step 1: Get the Necessary Ready

Ensure you have these handy things ready before embarking on the process to avoid inconveniences.

  • A screwdriver (for tightening and untightening screws)
  • Submersible pump
  • A five-gallon bucket
  • 2 washing machine hose
  • Two to four gallons of food-grade vinegar

Step 2: Doing the Setup

Take your vinegar-filled 5-gallon bucket and place it below your tank. Take one of your 2 washing machine hoses and connect one to your submersible pump.

Whether you have an electric or gas design, this is probably the perfect time you should ensure that you turn off the electrical power supply to avoid short-circuiting. This includes the line to the water heater (cold water supply line) and hot water supply to other home supply ends.

Step 3: Handling the Connections

Remember the hose you connected to the submersible pump? Take its loose end and attach it to the port that leads to the water heater.

It is advisable at this point to also connect the second hose to the discharge port of the water heater while directing its loose end to the 5-gallon bucket. Both the hose from the pump and that doing the draining should be directed to your bucket.

Notably, to avoid spills at the ports and have a smooth flow of water through the system, it is imperative to use isolation valves when doing the tightening at the connections ports.

Step 4: Let the Action Begin

Confirm that the setup is fine and proceed to open up the water inlet valve and the valve releasing the water. Connect the submersible pump and turn it on. It is important to make sure that your pump is in stable condition during this process.

In addition, make sure you check that the vinegar bucket is slightly positioned below the bucket with the vinegar. This will make it easy for you to monitor the vinegar distribution throughout the system as the flushing progresses.  Otherwise, turn off the valves and ensure the whole setup is done properly before resuming.

At this point, you can unscrew the ports tightening to check whether there could be any kind of sediment clogging at the ports.

Once you are satisfied, everything is working out fine, connect back the hoses and ensure the vinegar circulation is even. The hoses should be well-directed to the bucket to avoid uncontrolled and undesirable spills all over. You can let the flushing continue for about sixty minutes. This is usually the recommended time by most tankless water heater manufacturers.

Step 5: Winding up the Flushing

Once an hour is over, it is about time to turn off the pump. Your tank should be effectively cleaned by now. Run some cold water through the tankless water heater while the valve sandwiched between the pump and the water heater is closed.

This should take about seven minutes, my preferably time. Remember, you want to be sure any remnants that might be stuck in the tank are thoroughly cleaned. Let open the shutoff valve on the tank unit before doing all hose disconnections.

Step 6: The Strainer Clean Up

I never consider the water tankless heater complete unless the in-line filter is also clean. This is to help remove any kind of sediment that might be stuck in the strainer, use a cleaning agent that is not corrosive to the make of your strainer.

I recommend you let the whole unit dry up a little bit before reinstalling the filter. 20 minutes should be enough. Consider closing the cold water supply port before you detach the hose from the pump. Remember the vinegar drainage to the bucket? This is the right time to pour out its contents and clean it up.

See also – How To Clean Tankless Water Heater?

Step 7: Testing the Unit

For the flushing to be complete and satisfactory, this is probably the best time to open the cold water supply line through the tankless water heater.

Allow the water to flow through for about eight minutes to allow flushing again to clear away any kind of vinegar that might be stuck in the unit. Detach the hoses and let the supply line to the rest of your home resume as normal.

Turn the power supply back on. Test the water heater is functioning normally. Your tankless water heater should be flushed at this point. You can practice this with time as you become a novice in your own making in the long run.


By now, I believe you know how to flush a tankless water heater. Remember, it is essential to always read your unit manufacturer instructions and guide before carrying out the flushing. Flushing will always help with tank maintenance as you avoid tank malfunction that might not be under warranty cover. Ultimately, your water will be clean as you stay healthy.

See also – 5 Easy Steps For Tankless Water Heater Repair


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