How to Flush a Tankless Water Heater?

Over time, the calcium and debris build up inside the tank will start to grow and if not flushed time to time, that might create clogging issue and serve you dirty water. If your tankless heater is new, you might not face this problem soon but people who are using a tankless water heater for a couple of years they know the actual pain.

Flushing a tankless water heater is a challenge to most of the new owners. The thing is, it looks challenging which it is not actually. However, if you are looking for an in-depth guide on how to flush a tankless water heater, here it is. Stick to it and you will end up learning it!

Step by Step Guide to Flushing a Tankless Water Heater

Even the most complex step has been broken down to easy one so that you don’t face any difficulties understanding it. That being said, do not start the flushing process if you haven’t understood the process completely.

Understood? Okay, here we go!

Essential items

  • A bucket (5 gallons).
  • Two Stainless steel washing machine hose (2 pc)
  • Submergible pump.
  • Food-grade white vinegar (4-gallon)

Step 1

The first step is to shut off the heater. Check underneath the water heater you should see various color-coded handle levers. These levers are the key to shut off gas and water supply to the heater.

If your heather is on you see those levers are in-line with the pipe and when they are perpendicular, that means it is off. So make sure you turn that off! Turning all the levers perpendicular to the pipeline will close the gas inflow, water inflow, and outflow. And then, remove the power cord from the electric socket!

Step 2

Here you would have to remove the cold water service valve. You will find it above the colored levers. Since you have turned off all the gas flow and water flow, you can safely remove the valve.

The valve will have two sides, one is for cold water and another for hot and right before you remove the valve make sure to gather the bucket and the hose. And the reason is, the valve may trickle some remnant waters, don’t worry it won’t shoot. However, I am pretty sure you don’t want your floor to be wet. Unscrew the valve very slowly, when a small amount of water comes out you will know if that is cold or hot.

And not forget, there will be a small external pump attached to the bottom wall of the heater and no way water should reach there. Otherwise, it can create issues.

Pick the hose and put on end on the bucket. And immediately after removing the valve cap attach the other end of the hose so that the water can directly come to the bucket.  Once you have taken out all the cold waters, so the same with the hot water valve. Be careful, water could be hot enough to burn you.

Step 3

In the previous step, you have attached a hosepipe to the hot water service valve, that will help in this step as well. Here you have to add one more hose to the cold water valve and put the other end in the bucket. Empty the bucket that has water from the service valve. Bring the food-grade white vinegar.

Take the sump pump and add the cold water valve hose end that was on the bucket to the sump pump. Ensure that you have plugged the hose tightly.  Fill the bucket with vinegar and simply put the sump pump into it. The sump pump doesn’t have any on-off switch; it will start working when you plug the cord in the socket.

Plugin the sump pump and the vinegar with go in from the cold water valve and come out from the hot water valve. This circulation should go on for 60 to 90-minutes.

Step 4

Let the vinegar circulate and meanwhile, there is another thing you would want to do. And that is cleaning the air intake filter. The air intake filter is placed inside the tankless heater and reaching to there is also easy.

In order to reach the intake filter, you have to remove the face plate of the heater which is secured with 4 screws. Unscrew it and the inside of the heater will be exposed. Now locate the air intake filter and unscrew it.

Do not break it, after unscrewing it pulls is lightly towards you. If you have a water spout, turn it to the blast mood and shoot water at full speed on the filter. That should wipe off all the dirt. Wash it thoroughly and dry it completely before reinstalling it.

Step 5

Once the vinegar circulation exceeds 60 or 90 minutes now it’s time to rinse all the vinegar off from the valve. To do so, first, you would want to unplug the sump pump. And drain the vinegar. Do not drain vinegar on the grass, that will damage it. Instead of draining it on the toilet.

Remove the cold water valve hose and keep the hose attached to the hot water valve. From underneath align the lever that turns the cold water inflow on with the pipe. Now turn the heater on, you will see water coming from the hot water valve.

Fill a couple of buckets with the hot water, that much will be enough to clean off all the vinegar.

Step 6

It’s done! Now attach all the parts you have removed and align all the levers with the pipeline.

Frequently Asked Questions

Ques: How often should I clean a tankless water heater?

It depends on how dirty the water is, the dirtier the water is, the faster the dirt accumulation would occur. That being said, on average a tankless water heater should be cleaned once in a year.

Ques: Can I use CLR to clean my tankless water heater?

Cleaning the tankless water heater with CLR would be super easy and effective as well.


Remember what I said back, stick to the article and you will end up knowing how to flush a tankless water heater? Are you still here? Then you definitely know the exact process. Hope that helps!

Leave a Comment