Tankless Water Heater Maintenance

How to remove lime scale from a tankless water heater


Tankless, or on-demand water heaters, can deliver terrific benefits to the homeowner and small business. Their compact size, increased efficiency and flexibility are just a few reasons they are popular. However, as with any heat exchange method dealing with water, there are certain maintenance requirements to keep tankless water heaters performing at top levels. Millions of these units are in use today and as HVAC or plumbing contractors they offer a terrific opportunity for maintenance and repair services.

One of the ongoing maintenance requirements is to make sure that heat exchange elements are free from lime scale or scale as it is commonly know. This buildup is well known throughout our industry. What may look like a light coating of scale buildup can have serious impacts on the efficiency of the system, causing water heaters, boilers and more to run longer burner cycles. This leads to strain on the system and shorter lifespan. Not to mention the irate customers.

As with most situations, limescale buildup will differ based on the quality of the water being used, location, use amount etc. The following are general guidelines, but as usual, please check with the particular manufacturer of the tankless system if you have specific questions.

What you’ll need.


How to do it.


  1. Turn off electricity and gas (if applicable) to the tankless water heater.
  2. A good installation of a tankless water heater will include isolation valves in the in/out water connections. This is done for maintenance purposes. If there are no isolation valves installed, these must be added. Once added, close the water valves that connect to the main water supply and the home/business plumbing.
  3. Using a product like the BucketDescaler, attach the correct hoses to the isolation valves. This will create a closed loop between the descaler and the tankless water heater.
  4. Add your SpeedyBright limescale remover to the BucketDescaler as per the directions. For the BucketDescaler, we recommend a product like SpeedyBright, a mildly acid (phosphoric acid) scale removal agent that is specifically design for potable water systems. Most systems simply require a "one-shot" of SpeedyBright (1/2 gallon bottle) and 1 gallon of water added to the BucketDescaler.
  5. Open up the isolation valves between the tankless water heater and the BucketDescaler.
  6. Plug in the BucketDescaler to the power and turn the descaler system on. This will begin the circulation of the material in the tankless water heater and the bucket contents.
  7. Circulate the contents for approximately 20 minutes*. During this time you may see foam appearing in the bucket. This is an indication of the limescale cleaner at work, dissolving scale buildup on contact. Once the foam clears, that is generally a sign that the scale buildup has been removed.
  8. After completion of the descaling cycle, and with the pump still on, drain the contents of the tankless heater, hoses and pump by simply lifting the BucketDescaler out of the liquid in the bucket to pump air through the system. This will drain the liquid back into the bucket. Now turn of the pump.
  9. Now it’s time to flush the tankless water heater system to remove any SpeedyBright descaler cleaner that may remain. Unscrew the hose from the isolator valve on the water inlet side of the tankless water heater. Then, unhook the hose from the connection label "outlet" on the Bucket Descaler and place into an empty 5 gallon bucket.
  10. Slowly turn the isolator valve on the water inlet to allow water from the main water supply to enter the tankless unit. This will fill up the tankless unit and cause water to exit through the other isolator valve into the empty bucket.
  11. Using a pH testing strip or meter (SpeedClean P# SC-DS-pH-Paper) test the flow of water out of the tankless unit to make sure the water does not contain any descaler liquid (pH reading of <5).
  12. Dispose of used lime scale cleaner in accordance with any federal, state or local rules. After descaling, liquid and water should reach a minimum pH level prior to disposal, generally a pH of <7. This can be accomplished by adding water or other pH reducing agent like baking soda or soda ash.
  13. After flushign open the isolator valve of the hot water side.
  14. Turn electrical and gas mains back on and test the unit.
  15. Enjoy the benefits of a de-scaled tankless water heater!

*20 minutes is recommended time for a standard 1 gallon tankless unit with 1.5 lbs of scale buildup.