Maintaining Your Tankless Hot Water Heater - Removing Scale
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Maintaining Your Tankless Hot Water Heater - Removing Scale

The design of tankless water heaters increases the maintenance requirements over traditional hot water heaters, especially when it comes to the build up of scale inside the heat exchanger. The heat exchanger is where the water is heated by the hot gases inside the unit. Depending on the water quality in your area, mineral deposits can form on the interior surface of the heat exchanger and reduce its efficiency. Descaling is a procedure used to remove this build up which can be performed by the homeowner. This article will provide an overview of how to remove scale from your tankless water heater.

Most energy efficiency advocates will promote the fact that tankless hot water heaters save energy by not having to keep 40 or 50 gallons of water hot all of the time, but they may not actually save you money in the long run. The design of tankless water heaters increases the maintenance requirements over traditional hot water heaters, especially when it comes to the heat exchanger. The heat exchanger is where the water is heated by the hot gases inside the unit. Depending on the water quality in your area, mineral deposits can form on the interior surface of the heat exchanger and reduce its efficiency. Descaling is a procedure used to remove this build up which can be performed by the homeowner with a descaling kit and connection valves. If your home has a water softener you may not need to descale your tankless water heater as often or at all, but you should review the owner’s manual that came with the heater and follow the manufacturer’s recommendations. Every manufacturer recommends descaling, but there are several ways to perform this task.

Design of a Tankless Water Heater

Scale Build up inside a tankless water heater

Depending on the flow through the tankless heater, it may take several years for the scale build up to become excessive. Most heaters have a sensor built in to the heat exchanger to determine the level of scale build up that will cause an error code to display on the tankless water heater and lock out the unit. The heater will not operate until the unit the problem is corrected and the control panel is reset. Resetting a tankless heater without solving the problem will simply make the unit lock out again.

You may want to hire a professional plumber to descale your unit if you do not feel comfortable working on your heater.

Descaling

You should read and review the cleaning process for your particular unit and follow the instructions carefully so as not to damage the unit or void the warranty.  Depending on how your tankless heater was installed you may also need service connection valves which are usually not included in a standard descaling kit. After you purchase the kit and valves you will only need to buy the descaling solution for future jobs. A kit may cost between $100 and $200.

Service Valves are basically valves with an extra connection so that the supply lines do not need to be removed.

Typical Descaling Connection Diagram

In most cases the only tools you will need are an adjustable wrench, a 5 gallon bucket, and maybe a screwdriver. A smaller bucket and rags will come in handy as well to catch any drips if your unit is installed in a finished space or inside a closet.

Descaling Kit

  1. Disconnect power to water heater and shut off the gas supply if it is a gas-fired unit.
  2. Close hot and cold isolation and service valves and remove service caps.
  3. Pour 1.5 gallons of water into bucket and set it near the water heater.
  4. Most commercial descaling solutions will require the entire bottle be used per cleaning mixed with water, but follow the directions on your material. You can also try white vinegar or CLR but they may not be able to remove heavier deposits.
  5. Connect one hose to pump, and other end of same hose to cold service valve. Place pump in bucket.
  6. Connect second hose to hot service valve. Place other end in bucket.
  7. Open both hot and cold service valves.
  8. Plug pump into GFCI receptacle.
  9. Allow the pump to circulate the descaling solution through heater for 30-45 minutes. Unplug pump.
  10. Close cold service valve. Remove hose from cold service valve, and replace service cap.
  11. Disconnect the hose from the pump and remove pump from bucket. Dump out the used solution.
  12. Flush tankless water heater for 3-5 minutes or until water flows clear by opening the cold isolation valve and allowing water to exit through the hot service valve into a drain or bucket. You will need to empty the bucket several times.
  13. Close hot service valve. Remove hose from service valve and replace service cap.
  14. Open hot isolation valve.
  15. Connect power to water heater and return appliance to service.

Instead of descaling your unit frequently, you may be able to reduce the scale build up by installing an electrical scale removal system such as EasyWater or HydroCare or some similar system.

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Comments (4)

We have one of thes kind of water heaters and so this should be helpful. They are much different than the other kind.

This is one job I will be hiring out. Thank you for the alert of descaling.Promoted.

quite interesting thank you

Another great and informative share. thanks

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