What causes mineral buildup in tankless Water Heaters, and how to fix it?

A tankless water heater is an instant heater that heats water on demand. Because of its instantaneous function, no water remains inside the heater. Instead, it warms the flowing water on demand and gets rid of it.

Mineral buildup is the major problem with water heaters, whether it is tankless or with the tank. It means the tank is not the reason behind mineral deposition. The heat energy automatically separates minerals from water and causes scale buildup.

However, the buildup problem could be fixed using different mechanical and chemical methods.

What causes mineral buildup in a tankless water heater?

The following are the main reasons for mineral buildup in the tankless water heater.

·         Hard water

Water composition is one of the biggest issues behind mineral buildup in the tankless water heater. Usually, hard water contains high amounts of calcium and magnesium that are separated from water while the heating process. The separated minerals from the flowing warm water cause mineral deposition.

That’s why the hard water, with its high mineral composition, causes scale buildup even in instant heaters. The buildup will then affect the heating ability of the heater and will shorten its life span.

·         Debris-containing water filter

A water filter is the basic element of all kinds of water heaters. The major difference lies in its maintenance only. In tankless water heaters, a water filter with a small pore-size membrane is used. That’s why it needs regular cleaning to avoid any kind of buildup.

Most of the time, water contains debris and is collected at the filtration point. This debris-containing filter then allows hard water to pass through without mineral filtration. The mineral water, also with debris particles, starts accumulating in the tank and makes a scale buildup.

·         High temperature

The basic function of a water heater is to warm the cold water using heat energy. Heat energy is the main trigger behind mineral deposition. Heat or high temperature separates minerals from water.

Hence instant water heaters at a high temperature not only cause;

  • Mineral sedimentation but also
  • The burning of water heater because of high input intake and poor efficiency

The working of tankless water heaters at high temperatures and burning is directly related to mineral sedimentation. It is because sedimentation increases the energy intake demand of the heater.

·         Water flow

Water flow inside and outside the water heater greatly participate in mineral sedimentation. Instant water heaters have a narrow pipeline to get and deliver water. Because of the narrow pipes, the water flow becomes low, which is indirectly involved in;

  • Sedimentation of sand, debris, and minerals of hard water due to
  • The small heating amount of water at a high temperature
  • High temperatures separate the sediments from flowing water.

The slow flow rate assists the heat exchanger in attracting the minerals and properly removing them from the water. That is the reason the water flow does not only cause sedimentation inside the water heater but helps them to build up in the pipeline with the help of the high temperature of flowing water.

How to fix the mineral buildup problem in a tankless water heater?

Various normal and professional methods prevent the tankless water heater from mineral buildup.

Water softener installation

As hard water is one of the major problems of mineral sedimentation, hence the best solution is to install a water softener into the water heater. This action would be a precautionary measure because it ends up in the mineral deposition before it stars.

The softener will help in a way;

  • Installation in the water heater will remove the minerals without deposing them.
  • Installation in the pipeline will dissolve the sediments before the next incoming water flow.

It is the best way to fix the sedimentation problem and deal with hard water.

Regular cleaning of the water filter

A small-sized water filter used in a tankless water heater needs regular flushing because of the hardness of flowing water.

The filter removes debris and other sediments from the incoming water to avoid scale buildup in the water heater. Depending on the water composition and usage of the water heater, the filter requires routine maintenance.

Regular cleaning will protect the water heater from overloading, which will further avoid high energy input. It will then improve its efficiency and increase its life span.

Chemical treatment

It is an effective method to chemically treat the sedimented water heater. Chemical directly degrades the minerals and other deposits and will clear the surface of the heat exchanger.

Chemical treatment is a two-step process;

  • Add chemicals to the water heater similarly as the flowing water enters the heater and retains it inside the instant heater for an hour.
  • After removing the added chemical again, flush it with the chemical. This time only flow the chemical from the heater and pipeline just to ensure the cleaning.

Temperature maintenance

Maintaining the major function of an instant water heater would be the best sedimentation-controlling factor. Higher temperature is the solid reason behind mineral buildup, even in the tankless water heater.

Keeping the heater at its normal or optimum temperature will reduce mineral separation from hard water.

Temperature maintenance will clean the heat exchanger from mineral deposition and protect the heater from burning. The routine temperature maintenance of the water heater will enhance its efficiency and, most importantly, avoid further sedimentation.

Regular flushing of tankless water heater

Usually, water heaters with tanks require proper flushing once a year, but tankless water heater demands regular flushing.

Regular flushing will protect the heater from the stress of overloading and the consumption of a high amount of energy. It will further protect it from mineral deposition and burning of the heater and will increase its working efficiency.


Mineral buildup is a serious problem both in tank less and with tank water heater. Water composition and the amount of heat lead to mineral deposition. The sedimentation could be fixed by regularly maintaining the basic function and elements of the tankless water heater.

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