How and When to Descale a Tankless Water Heater – Step by Step Guide

Tankless water heaters have proven to be the most efficient water heating units in recent times. These units last longer with lower running and maintenance costs. Those who have these units installed in their homes must have got this question popping up in their minds often that How to Descale a Tankless Water Heater?. Well, the process is pretty easy and you can do it yourself at home by following some simple sets. But we recommend getting it done by a professional plumber to avoid getting into any trouble.

The tankless water heating units have proved to be very helpful for fulfilling daily hot water needs. These compact units can fit into any small space. A tankless water heating unit can last for about 20 years with proper maintenance. The process of descaling or flushing the tankless heating unit is simple and can be done by the user himself at home. It’s important to know how to perform the descaling procedure.

Process of Descaling a Tankless Water Heating Unit

Is your water heating unit installed in a wall? To give the unit access to water and other pipes it is installed in the wall. To descale such a unit you might need to take help from a professional plumber. The presence of a professional makes the task much easier. If you are eager to do the process yourself then here is what you need to get started and get it done.

Before starting the descaling process please cut off the electric or gas supply to the heating unit. Also, make sure to stop the water supply to the heater. Make sure to remove the caps from the service valves as well.

Equipment Needed to Start the Process

  • 2 hosing lines
  • White vinegar
  • Bucket


  • Accessing the unit

Some tankless water heaters have an outside covering to protect the connections. This covering needs to be removed in order to access the unit for descaling purposes. Some units don’t have such a covering.

  • Check for flushing valves

Tankless water heating units have flushing valves installed. Check your unit for these valves. If you are not able to find them then call your local plumber and ask him to get these installed for you.

  • Cutting off the gas supply

If your tankless water heating unit is fueled by gas then you need to cut off the gas supply first. This involves turning the valve perpendicular to the fuel supply. This step is most important to avoid any hazards during the descaling process.

  • Disconnecting the water supply

Disconnect the water supply by turning off the water supply valve. Disconnect the cold water valve the supplies cold water to the water heating unit for heating. Also, disconnect the hot water valve the supplies water outside through the faucet for daily use.

  • Connecting the hoses

Remove the caps present on top of your flushing valve. This helps remove any built-in pressure. Connect the hose tightly to the flushing valve. Make sure the connection is tight enough so the detergent solution won’t leak out. Rubber washers are used to prevent such leakage.

Turn the flushing valve on by rotating it to a perpendicular position to the hot and cold water valve. Close the output water valve and instead turn on the purge valve. Choose the correct hosing line.

  • Filling bucket with a cleaning solution

Put the vinegar or detergent solution in a bucket and use the pump to circulate the cleaning solution through the water heating unit. Carry on this process for 30 minutes if you have a cleaning solution or for 3 hours if you are using vinegar to descale the water unit. After you have completed the mentioned time now get a bucket of clean water. Use the same pump to circulate the water through the pipes. Keep pumping this clean water into the pipes until the returning water also becomes clear. When the water returning from the unit is clear discard the remaining cleaning solution.

  • Cleaning the sediment filter

A sediment filter is present on the cold water inlet to prevent the water sediments from reaching the heating element. The solids can build up inside the sediment filter. Unscrew the filter and use a brush to thoroughly clean it. The presence of sediments inside the filter hinders water flow through the inlet valve.

  • Reconnecting water and fuel supply

Disconnect the hosing line from the water heater and close the purge valves of the unit. Make all the connections again and connect your unit to the water supply again. The unit is ready to heat the water up to the required temperature.

Why Opt for Professional Help?

If you are not able to properly descale the unit you might end up leaving harmful chemicals that will mix with the drinking water. The presence of harmful cleaning chemicals in your drinking water will make the water harmful to your health. At other times you might forget to turn on a valve which also results in improper functioning by the unit. You will need to disassemble the unit again and then properly clean any leftover cleaning solution. To avoid any such discomfort from occurring you can ask a professional plumber for help. They will provide a quality service at an affordable price.

Air Filter Maintenance

Uncover your water heating unit to access the air filter. This filter is mostly located on top of the water heating unit. Once you know where the water heater is remove it to look for any dirt that has to build up inside it. Use a soft brush with a soapy solution and a piece of cloth to clean it. Once all the dirt is removed use clean water to wash away the cleaning solution. Use a cloth to pat the filter dry. Let the air filter dry in the open air and then place it back into the unit.

Cost of Descaling a Tankless Water Heating Unit

Self Cleaning a tankless water heating unit is an easy task. It is not an expensive process at all. You need to know some basics about your water heating unit and the process will become easy peasy for you. If you want to get professional help from a plumber then this process might become a little expensive for you. Doing the descaling job yourself will save you a lot of money.

Once you have gathered all the necessary equipment next you need to be ready to invest about 2 to 3 hours into the process. Although this is an easy process yet it will take a considerable amount of time to get done.

Why do Tankless Water Heaters Need Descaling?

Tankless water heaters need a lesser amount of energy to work as compared to the previous units. They are also less space occupying which is a helpful feature for those already living in small spaces. They do need maintenance like all other devices but once a year. This annual maintenance prolongs the life of the unit. This is the reason why it’s recommended to descale the unit every now and then. To be able to do the process of how to descale a tankless water heater properly you just need to follow the above process that we have discussed in this article.

Reason for Scale Build-up in a Tankless Water Heating Unit

If you are replacing a traditional water storage unit with a tankless then you will be already familiar with the need of flushing the unit every now and then to prevent sediment buildup. The traditional water heaters are also prone to damage resulting from mineral buildup. This buildup can lead to an explosion too. In the case of a tankless water heating unit, the build-up won’t result in an explosion but irreparable damage of some parts might result.

The heat exchanger is the most sensitive part of your water heating unit. If the sediment builds it will lead to more energy requirements for heating. And the limestone buildup ends up permanently destroying the heat exchanger. Thus the whole unit becomes useless.

When to Descale a Tankless Water Heating Unit?

Once every year descaling is important for optimal performance by the unit. This will prevent the sediments from building up inside your unit and clogging the valves. The good news is if you have a soft water supply you won’t need to descale your unit that often. If you are still confused about how often you should descale your unit then ask a plumber to help you out.

Is the Annual Descaling of the Water Heating Unit Worth it?

Tankless water heating units have proved to be a better investment than the traditional storage-type water heaters. This is cause they have higher running costs. The initial installation cost of a tankless unit will be much higher but in long run the benefits of a tankless water heater out way the initial cost. According to studies, these units are about 30 percent more energy efficient. The maintenance process is totally worth it cause if properly done it prolongs the life of the unit to about 20 years. High-level maintenance may help the unit last for even up to 30 years.


Leave a Comment