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How To Flush Your Tankless Water Heater


Investing in a tankless water heater is a decision that can bring significant benefits to your household. Unlike traditional tank-based water heaters, tankless models offer several advantages that enhance both efficiency and convenience. One of the most notable benefits is their cost-effectiveness. Tankless water heaters are generally more energy-efficient, as they heat water on demand rather than continuously heating and storing it. This on-demand heating means they use less energy, which can lead to lower utility bills.

Another advantage of tankless water heaters is their compact size. Unlike traditional models that require a substantial amount of space for the tank, tankless heaters are much smaller and can be easily mounted on a wall, freeing up valuable space in your home. This makes them an ideal choice for smaller homes or apartments where space is at a premium.

To maximize the benefits of your tankless water heater, it’s crucial to understand its maintenance, particularly how and when to flush it. Regular flushing is essential to remove any mineral build-up inside the unit. This build-up can occur over time, especially in areas with hard water, and can affect the heater’s efficiency and longevity.

Learning how to flush yours is the first step towards getting the most out of it while saving on energy. However, it would be best if you also learned when to flush it and the tools required to make the process seamless, safe, and effective.


Reasons Why You Should Flush Your Tankless Water Heater

Traditional heaters often get flushed to eliminate sediments from the water supply. It would help if you did the same for your tankless heater to reduce the risks of blockages and inefficiency. Water also consists of salts like calcium and magnesium sulfate, which can cause scale buildup. Even though a tankless heater’s explosion risks are small, this scale forms an insulating layer that causes poor heat exchanger efficiency. In addition to higher power bills, scale reduces the heater’s lifespan. Moreover, most warranties do not cover damage due to scale buildup.

How Often Should You Flush Your Tankless Water Heater?

Maintaining your tankless water heater is crucial for ensuring its efficiency and prolonging its lifespan. Flushing your tankless water heater at least once or twice a year is a key part of this maintenance. Over time, minerals and sediment from water can build up inside the heater, particularly in areas with hard water. This build-up can reduce the efficiency of the heater, as it has to work harder to heat the water, and can also lead to increased wear and tear.

If the water in your home is of poor quality, particularly if it’s hard or has a high mineral content, it’s advisable to flush your tankless water heater more frequently, perhaps twice or thrice annually. This is because hard water can lead to more rapid accumulation of minerals and scale inside the heater, which can not only reduce its efficiency but also shorten its lifespan.

To further combat the effects of hard water, you can add a sediment trap and a water softener to your plumbing system. A sediment trap, installed on the water line that feeds into your tankless heater, helps by catching sediment, debris, or particulates before they enter the unit. This can be particularly beneficial in areas where the water supply may carry a lot of sediment.

In addition, a water softener can be an invaluable addition to your home plumbing system. It works by removing minerals like calcium and magnesium from the water, which are the primary culprits behind hard water. By softening the water, it not only protects your tankless water heater but also benefits your entire plumbing system. It helps in preventing scale build-up in pipes and fixtures, enhancing the performance and lifespan of appliances like dishwashers and washing machines.

By flushing your tankless water heater regularly and considering the installation of a sediment trap and water softener, you can significantly improve the efficiency and longevity of your water heater. These steps help in ensuring that your tankless water heater operates at peak efficiency, providing you with continuous hot water while also saving on energy and maintenance costs in the long run.

Tools Required When Flushing A Tankless Water Heater

You will need a submersible pump for flushing. Since you will not have to remove massive amounts of water to remove the sediments like a tank heater, the pump will save you time. You will also require a large bucket(5 gallons). You can also consider a flushing kit with all the items needed: a submersible pump, bucket, hoses, and a descaler. This once-in-a-lifetime investment should make home water heater plumbing easier and more effective.

Steps To Effectively Flash A Tankless Gas Water Heater


1. Disconnect the heater’s power
2. Detach the access panel and use a non-contact voltage tester to be sure that no more power is flowing to the main terminal
3. Shut off the gas valve
4. Find and close both the hot and cold shutoff valves so that no water enters the heater as you flush it
5. Find the hot water pressure release valve on the hot water line and open it to release residual water. Do this safely, as the water will be hot.
6. Join hoses to the cold water service port as well as the hot water service port.
7. Put your submersible pump in the bucket listed earlier, connect the cold water service port hose to the pump, and ensure that you free the end of the hot water service port hose into the bucket
8. Pour four gallons of pure food-grade white vinegar in the the bucket


1. Open both the cold and hot water service ports and turn the pump on
2. Allow the vinegar to circulate in the heater for at least one hour. Allow it to go longer if your pump ruins less than four gallons per minute. Vinegar should remove the sediment and break down the dirt buildup.
3. After vinegar circulation, turn the pump off and discard the vinegar
4. Turn off the cold water service port and detach the attached hose, then the cold water shutoff valve to remove any residual vinegar from the heater system in the basin or bucket for about ten minutes.
5. Close the cold water shutoff valve
6. Allow the the water to finish draining, remove the hose attached to the hot water service port, then remove its hose.
7. Detach the cold water inlet filter and the hot water filter, then flush them in a sink to remove the materials they have collected over time


1. Return respective filters securely, then open the hot and cold water shutoff valves
2. Reattach the access panel
3. Open the gas shutoff valve
4. Reconnect the electrical supply

Flushing An Electric Tankless Water Heater


1. Shut off the power supply at the main circuit breaker
2. Close the cold water shutoff valve
3. Open the faucets so that any water within the unit drains
4. Close the hot water shutoff valve
5. Remove the access panel and use a non-contact voltage tester to ensure that there is no power flowing to the terminal
6. Detach the wires from the heating element, then loosen the hexagonal brass top of the heating element counter-clockwise to remove it from the unit. Here, consider examining the element for any signs of damage. If you spot any cracks, replace the element immediately for your safety.
7. Place the heating element in the heater’s cooper chamber to get cleaned.


1. Fill up the heater’s cooper chambers with undiluted food-grade white vinegar and let it sit there for two hours. The vinegar will break down the scale on the parts inside the chamber.
2. Drain the vinegar and discard it
3. Reattach the heating element, then reconnect the wiring to the element
4. Open the cold water shutoff valve, then open the hot water shutoff valve
5. Turn off some hot water faucets and let the water run for about five minutes to remove all vinegar traces and clear any air pockets from the lines


1. Turn off the hot water faucets
2. Close the cold water shutoff valve
3. Remove the cold water inlet filter and clean it at a sink to remove debris trapped over time
4. Return the filter
5. Close the access panel and turn the power back on at the circuit breaker



The process of flushing your water heater, whether it’s powered by gas or electricity, is a relatively simple and quick task that most homeowners can undertake without it becoming a days-long project. This routine maintenance is crucial for ensuring that your water heater operates efficiently and has a long service life. Flushing the heater helps remove sediment that accumulates over time, which can hinder its performance and efficiency.

Despite the simplicity of the task, there might be situations where you require more technical assistance or prefer professional servicing of your water heater. This is where King Heating comes into play. Our team of experienced professionals is equipped to handle all aspects of water heater maintenance and servicing. Whether you are unsure about performing the flush yourself, need help diagnosing a problem with your water heater, or simply prefer the assurance that comes with professional service, King Heating is at your service.

We understand the nuances of both gas and electric water heaters and can ensure that your unit is not only flushed correctly but also checked for any potential issues that might affect its performance. Our technicians can provide a thorough inspection, identify any areas of concern, and perform necessary repairs or adjustments to ensure your water heater operates at its best.