How To Protect Tankless Water Heaters From Hard Water

Hard Water

Hard water can play havoc with a tankless water heater and being aware of your risk can not only save you money but also a major headache. Different geographical areas experience different levels of water hardness, which is determined by the amount of dissolved minerals within the water supply.

Water that is relatively pure and mineral free is called soft water. Rain water would be considered soft water, but as it's absorbed into the ground the water travels thru soil and rock. Eventually, it finds its way to rivers, lakes and other bodies of water.

As the soft rain water travels to its destination, it begins to absorb minerals from the ground. The more minerals the soft water absorbs, the harder the water becomes. Hard water contains a high concentration of natural minerals, calcium carbonate and magnesium in particular. 

As the water passes over surfaces within your home, these minerals will begin to separate from the water. Over time, the separated minerals will form a scaly layer called limescale. Sinks, dishwashers, washing machines, and even showers are all prone to limescale build-up. ​

  • Although not a health concern, hard water causes problems for many home appliances. 

Why Descaling your Tankless Can Save it from Hard Water

Both tankless water heaters and traditional water heaters are negatively impacted by limescale build-up. But with tankless systems  the unit's heat exchanger will need to work harder than necessary to heat the water. This is because the heat exchanger will become caked with limescale which will prevent it from transferring heat as efficiently.  

Here are some of the affects of limescale:​
  • The heat exchanger will need to work harder to heat the water because it is caked with limescale. It will eventually overheat.
  • The heat exchanger will not reach it's service life potential and need to be replaced.​
  • An error code could be triggered to shutdown the unit. A professional plumber will need to be called to get the unit up and running again.
  • As the limescale built-up increases the heat exchanger's burner cycles also increase to compensate for the lost efficiency. The tankless is no longer saving money on your fuel bills due to the lack of efficiency. 
  • Manufacturer warranties do not cover damage caused by limescale build-up.

Flushing a tankless water heater is critical to keeping it operating and reaching it's service life potential. Manufacturer recommendations vary, but most suggest every 12 months.​ But in the end, the frequency should be determined by the homeowner and the decision should largely be based on the area's water hardness. You can purchase these inexpensive test strips to check the mineral content of your water. 

Solutions to Hard Water Problems

Certainly flushing your tankless can remove limescale from the unit after it's already formed, but there are ways to reduce the amount of minerals within your water to help prevent the build-up in the first place. Here are some methods to take a pro-active approach to hard water:

Scale Inhibitor System

A scale inhibitor system is a relatively inexpensive way to protect water heaters from hard water. This system installs a filter on the water heater's incoming water supply. A shut off valve should be installed on the pipe on each side of the filter to make changing the filter easy.

As the water enters your home, it passes thru the scale inhibitor filter BEFORE it flows into the water heater. This type of filtration system will reduce the limescale build-up by preventing the minerals from bonding to metal surfaces.  

Aqua-Pure AP430SS Hot Water System Protector
  • Binds calcium and magnesium hardness minerals, preventing them from precipitating out of solution and building up on metallic surfaces
  • Inlet/Outlet Size:3/4 inch NPT,Dimensions height 10 1/4 inch(26.0),Diameter 2 3/4 inch.Contains siliphos, a 100% Pure FOOD Grade scale inhibitor approved by usda
  • Stainless Steel head
  • Flow rate 6 gallons per minute
  • Max operating Temp. 100F
Watch the Video on The Scale Inhibitor System

Salt Based Whole-House Water Softener

Both salt based and salt-free water softeners are a good fit for areas with extreme hard water. All of the incoming water to the house is treated, both hot and cold, so all of your appliances, fixtures and plumbing will benefit.

Salt based water softeners are probably the most affordable way to treat water. These systems will completely remove the calcium and magnesium from the water as it passes thru the water softener.​

Calcium and magnesium is replaced with sodium ions, which is done by binding negatively charged potassium, sodium or hydrogen resin to positively charged metal ions. The hard minerals are literally drawn from the water. ​

As hard water enters your water softener it flows thru resin beads. The resin beads attract and trap the hard mineral molecules, and as the water enters your home, it is mineral free and considered soft.

Over time the resin beads eventually are "full" of hard water minerals. In order for the system to continue to soften your water it needs to run thru a process called regeneration.

Fleck 5600 SXT Water Softener Ships Loaded With Resin In Tank For Easy Installation (48,000 Grains, Blue)
  • Manufacture 5 year warranty Valve/ 10 year warranty Tanks
  • Comes standard with Uprgarded Paddle Wheel Meter
  • Ships with resin pre loaded in fiber glass mineral tank for easier installation
  • Free Upgraded Paddle Wheel Meter
  • Made In USA Structural Tank Ships Loaded With Resin In Mineral Tank for easier installation
Watch the Video on Salt Based Water Softeners

Salt Free Whole-House Water Softener

Salt free water softeners are also commonly called water conditioners or scale inhibitors. They function very differently than salt based water softeners as the hard water minerals are not removed from the water. 

They do, however, still help prevent limescale build-up. Here are the 2 common types of salt free systems:​


The process used in these systems is called epitaxial crystallization, where the calcium is changed from a type that deposits limescale, to a type that does not. 

The minerals are not removed from the water, but rather are allowed to pass thru in a stabilized state making them unable to form limescale. 

Nuvo H2O Dphb-a Home Water Softener System, 5 X 24" - New Model - No More Hard Water by Using Revolutionary Technology!
  • The NuvoH2O Home system uses revolutionary technology to lower the PH level of water
  • Resulting in water that is soft and healthy for all of your household uses, including drinking, bathing, washing, and lawn and plant watering.
  • Home System is designed for Homes 1,000-2,000 square feet.
  • Water flow: 12-15 gpm with 1" ports (no change to existing water flow)
  • Capacity: Approximately 35,000 gallons per cartridge
Watch the Video on Catalytic Salt-Free Water Softeners

Electromagnetic systems alter the ions of the hard water minerals as the water flows thru a magnetic field. Many homeowners like that there are no chemicals used in the process of treating the water and that the system is very easy to use. Many systems can be used on both metal and plastic pipes. There is, however, some debate on their effectiveness.

Eddy Electronic Water Descaler - Water Softener Alternative
  • 12 month 100% "no quibble" Money-Back Guarantee + Lifetime Repair or Replace warranty.
  • Easy customer installation on metal or plastic pipes. Helps prevent build-up of lime scale and dissolve existing deposits.
  • No salt alternative to a water softener. Emulates softened water without changing your water hardness. Retains healthy minerals in your water supply.
  • Descales entire water system. Maintenance-free with great results up to and above 20 gpg.
  • Environmentally friendly. No salt added to your water and users report great improvements to hair and skin. Please scroll down page to see full Product Description.
Watch the Video on Electromagnetic Salt-Free Water Softeners

Last update on 2018-08-14 / Affiliate links / Images from Amazon Product Advertising API