Do tankless water heaters have to be flushed annually?


Do tankless water heaters have to be flushed annually?

Asked by Joan

The unit is a Takagi TK-3 model.

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Scott Johnson's picture

Good question.The answer is it's a good idea to do so annually.

  • There are those who will tell you it's not necessary, but I believe those are the same individuals who change their motor oil every 30,000 miles.
  • Scale buildup in the heat exchange on most tankless units is not covered under manufacturers' warranties.

Flush at six months?

Sometimes it may be wise to do it every 6 months. That answer is determined by a few factors:

  1. How hard the water is in your area
  2. How high the W/H temp is set
  3. Volume or amount of water heated.

In locations with hard water, the risk of scaling in the form of calcium, lime, minerals and such, is greater at temperatures over 120 degrees Fahrenheit. Make sure to set the water heater below that temp. A good rule of thumb is that for every 20 degree F increase above a 120 degree Fahrenheit set-point temperature, the amount of water scale buildup is doubled. Yikes!

Those statistics also apply to all types of water heaters. However, in any glass-lined (porcelain) water heater, the glass become porous at temps above 140 degrees. Porous glass, not good...

How to flush the Takagi unit

The Takagi unit, as most, should have a filter at the cold water inlet. Clean this as needed. If the the unit has cleaning bypass valves, great. If not, have some installed.

A 5-gallon bucket, small sump pump, 2-gallon supply of white vinegar, and 1 hour is all you need. Most of these units will last well over 20 years if properly maintained.

Best part is... you can do this yourself, if so inclined.

For more information:

Read Evan Little's Q&A "I'd like to be able to flush my tankless water heater to remove scale. What type of circulating pump do I need?"