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How to Descale Tankless Water Heater? [8 Important Steps To Follow]

With tankless water heaters, calcium build-up is much less of a problem if compared to a traditional tank-style water heaters. However, they still need regular maintenance, especially in areas with hard water. Perhaps you have read a lot of guides on how to descale tankless water heater around the internet.

Don’t worry, descaling your water heater is not hard to do and you can definitely do it by yourself. Since plain white vinegar is all you need, tankless water heater maintenance costs are low. Read this guide to learn how to do it. It will take approximately 60 to 90 minutes of your time to finish the whole process.

Just in case that if you are wondering how often should you descale your water heating unit, once a year is probably a good measure. However, if you live in an area with very hard water, you may need to do this more often. Some water heaters have built-in indicator which tells you when the unit needs maintenance work to do.

Things You'll Need

Here is what you will need in order to descale your tankless water heater:

How to descale my tankless water heater
  • A five-gallon bucket
  • Two drain hoses (in most cases they need to have a ¾-inch connection 
  • A submersible pump
  • 4-gallons white vinegar

You can also opt to buy the hoses, the pump, and the bucket all together in the form of this “tankless water heater flushing kit”.

8 Important Steps To Descaling Tankless Water Heaters

1. Turn off the unit

If you are using an electric water heater, find the electrical circuit for the unit at your breaker panel and turn it off. You can check if the power is turn off on the unit itself just to be safe.

To do this, you’ll need to access the wiring by removing the cover plate. Take a non-contact electrical tester and hold it against every wire going into the terminal. If it lights up, you haven’t turned off the power completely. Never try to descale your unit without turning the power off! This can cause serious damage to the unit.

If your heater runs on gas, you’ll just need to turn the gas valves off by rotating them counterclockwise.

2. Turn off the water supply valves

You’ll need to turn off both the cold water valve and the hot water valve. They are most likely located below your water heating unit. Some heaters will also have a service valve or a draining valve which you can use to drain any water remaining inside.

3. Connect the hoses

Take one hose, and attach one end to the cold water valve (the blue one). Attach the other end to your submersible pump. Connect the second hose to the hot water valve, and let the other end of this hose go into your bucket. Before you move on, make sure that all the connections are properly tightened.

4. Time for vinegar

Fill your bucket with 4 gallons of white vinegar. Place the pump in the bucket together with the other end of the hose coming from the hot water valve.

5. Turn on the pump

Open the valves for the hot water on your unit and turn the pump on. In many cases, these pumps don’t have an on/off switch. They just need to be plugged into the wall.

For this reason, make sure to place the pump into the bucket first and then plug it in. Leave it running for 45 minutes so the vinegar can circulate. When the time is up, turn off the pump and let the vinegar drain out the water heater and into the bucket.

6. Clean the air intake filter

Flushing your water heater is also the perfect time to clean your air intake filter. It’s located inside the unit, but it’s usually not hard to get to it. Consult your user manual to see exactly how to remove the inlet screen, as the instructions might vary according to the model. Rinse the screen and put it back in place.

7. Rinse your water heater

By now, all of the vinegar should have drained out into the bucket. Throw it away. You should now remove the pump and the hose that was attached to the cold water valve (the hot water hose stays on). Put the cap back on the service valve.

Turn on the cold water and let it flow through your unit and into the bucket until the bucket is almost full. (Be sure to turn off the cold water in time, so you don’t overfill the bucket).

8. Your water heater is ready to be turned on again

Congratulations, you have descaled your water heater! Reattach all of the connections and check if everything is tightened properly. Turn on the power or the gas, and check if the hot water is running again. If you have done everything right, your unit should be working normally.

Other Types of Applications:-

  • Click here if you are looking for tankless water heaters that provides radiant floor heat.
  • Check out this article if you are looking for tankless water heaters that can be used under sink.


We certainly hope that you enjoyed our guide and fount it useful. Do keep in mind that you should at least descale your water heater once per year so that your unit can perform at its best to deliver optimum result and increase its durability. 

    Verner Ellen

    Hi, my name is Verner Ellen. I am a homebody whose interest is in getting the best home tools and equipments to help with the the everyday house chores. I also love fitness, cooking and grilling. Maintaining a clean and comfortable home is my lifelong passion.