How to Flush a Tankless Water Heater

flushing a tankless water heater

If you've got a tankless water heater in your home, you probably love the energy efficiency. You might have been too busy counting your dollars saved to realize that this remarkable technology does require a little maintenance. Did you know you need to descale your tankless water heater? Follow these instructions if you don't know how to flush a tankless water heater. For this project, you're going to need vinegar, a submersible pump, and appliance hoses.

How Often Should I Descale a Tankless Water Heater?

You might want to ask a local plumber about what's normal in your area (water conditions are a factor to consider), but the general rule of thumb is once a year. Here is how you get the job done:

How to Flush a Tankless Water Heater

  1. Turn off the water heater - if it's a gas water heater, then just set it to the off position. If it's electrical, you must cut the power to it at the breaker. If you are not sure which breaker is the right one, either run a test with a non-contact electrical tester or just cut the power off to the entire house.
  2. Cut the supply of water - close the inlet valve that supplies the on-demand water heater with cold water and close the outlet valve that supplies the home with hot water.
  3. Connect hoses to each isolation valve - it's easiest if you have two short hoses (about 6 feet, preferably appliance hoses). The first hose to the cold water isolation valve should connect to a pump (it can be a pond pump or a sump pump). The second hose to the hot water isolation valve will be submerged in the bucket of the descaler you are about to prepare.
  4. Fill a 5-gallon bucket with distilled white vinegar - place the pump within the bucket before filling it. Make sure the bucket is clean first.
  5. Open both isolation valves and turn on the pump - let it run for about 45-60 minutes.
  6. Turn off the pump - let all the vinegar drain into the bucket, then close the cold water isolation valve.
  7. Flush the vinegar - take your second hose out of the bucket and point it down a drain or outside. Open the cold water supply valve and let it run for 5-10 minutes, then close it.
  8. learn how to descale a tankless water heater with these components
  9. Remove the hoses - and don't forget to close the hot water isolation valve.
  10. Clean the inlet feature - read more about this further down the page.
  11. Open supply valves - open both the cold water supply inlet and the hot water supply outlet.
  12. Turn the water heater back on - run it and check for leaks and allow air to be pushed out of the lines to your fixtures.

If you prefer a youtube tutorial, try this Tarek's DIY video.

How to Clean a Tankless Water Heater Inlet Filter

For proper cleaning, you can't forget to take a minute to tidy up the filter screen. Refer to your owner's manual because, in some cases, there are two filters.

  1. Locate the filter with your manual.
  2. Flush the filter with tap water.
  3. Replace the filter.

The Plumbing Experts at PlumbersStock

If you have questions about your DIY project, check out our helpful water heater FAQs and tutorials. If you already know what to do and what you need, then shop our website for water heater parts or accessories. Take advantage of great deals, and if you can't find what you need, don't hesitate to contact us. We carry the best brands, including Bradford White, Noritz, and Takagi.

Related resources:
How to Reset a Tankless Water Heater
Ventilating for Tankless Water Heater
How Long Do Tankless Water Heaters Last?

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