What Size Pump To Flush Tankless Water Heater: A Complete Guide.

The size pump needed to flush a tankless water heater depends on the manufacturer’s recommendations and the water pressure in your area. Usually, a small submersible pump is sufficient for the job.

When it comes to maintaining your tankless water heater, flushing it periodically is essential to remove any build-up of sediment and minerals that can cause clogs and damage. However, the size of the pump you need to flush it will vary depending on several factors.

Firstly, you should always follow the manufacturer’s recommendations for your specific model of tankless water heater. Secondly, you’ll need to consider the water pressure in your area because this will affect the flow rate of the pump. In most cases, a small submersible pump is sufficient for the job, and you can typically rent one from a hardware store or plumbing supply company. In this article, we’ll take a closer look at the factors that affect pump size and how to choose the right one for your tankless water heater.

What Size Pump To Flush Tankless Water Heater: A Complete Guide.

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Understanding The Importance Of Flushing A Tankless Water Heater

Tankless water heaters have grown increasingly popular over time due to their energy efficiency and convenience. They are also known as on-demand water heaters as they heat water only when needed instead of storing hot water in a tank. Although tankless water heaters have several benefits, there is one critical aspect that most homeowners fail to consider- flushing the system regularly.

In this guide, we will discuss why flushing is crucial for tankless water heaters, and how often you should flush them.

Introduction To Tankless Water Heaters

Tankless water heaters are an innovative type of water heating system that heats water on-demand, ensuring an immediate and continuous supply of hot water. They come in various sizes and can be powered by either electricity, propane, or natural gas.

Tankless water heaters are becoming increasingly popular due to their excellent energy efficiency and longevity when compared to traditional water heaters. These systems take up minimal space, typically last longer than tank-type water heaters, and reduce standby losses.

Why Flushing Is Important

Flushing a tankless water heater is essential to ensure the unit functions correctly, maintains optimal performance, and prolongs the system’s lifespan. Failure to flush your tankless water heater periodically is detrimental to its functionality and can cause problems such as:

  • Build-up of sediments: When hard water flows through the heating chamber, deposits of calcium and magnesium can accumulate, causing a reduction in water flow and efficiency. Sediment build-up can also cause corrosion and damage to the system’s internal parts, resulting in costly repairs.
  • Reduced efficiency: Sediment build-up can also affect the system’s efficiency, as the heater may need to work harder to heat water.
  • Foul odors or taste: Stagnant water containing sediments can emit unpleasant odors, and in some cases, affect the water’s taste.
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Frequency Of Flushing

The frequency of flushing your tankless water heater depends on several factors, such as the hardness of your water, the system’s usage, manufacturer’s recommendation, and local regulatory requirements. At a minimum, it is recommended that you flush the system once a year to remove any sediment build-up.

If you live in an area with hard water or heavy usage, you may need to flush your tankless water heater more frequently. Consult with your local plumber or refer to the manufacturer’s guide for specific instructions.

Flushing your tankless water heater is essential to maintain the unit’s performance, prolong its lifespan, and ensure that you continue to enjoy the benefits of this innovative system. By adhering to the manufacturer’s recommendations and consulting with your local plumber, you can avoid costly repairs and enjoy an endless supply of hot water.

Remember to flush your tankless water heater periodically to maximize its efficiency and functionality.

Choosing The Right Pump For Your Tankless Water Heater

Tankless water heaters offer several benefits over their traditional counterparts, including energy savings, longer lifespan, and efficient water flow. However, to maintain proper functionality, a consistent flow rate is necessary. That’s where a pump comes in! In this section, we’ll discuss the importance of selecting the right pump for your water heater and the factors to consider when doing so.

Why Use A Pump?

If you own a tankless water heater, you may be wondering why you would even need a pump in the first place. Well, a pump is essential in maintaining a consistent flow rate as some tankless heaters require a specific flow rate to operate correctly.

Without the right flow rate, you can expect to experience inconsistent hot water flow, which can lead to a reduction in the heater’s lifespan.

Factors To Consider When Choosing A Pump

When selecting a pump, several factors need to be taken into account. Here are some of the most crucial aspects to consider:

  • The pump’s flow rate – choosing a pump with the proper flow rate is essential. Ensure that the pump can deliver the required flow rate for your tankless water heater.
  • Head pressure – the amount of head pressure the pump can generate is also crucial as it determines how much water can be pumped through the system. Choose a pump with enough head pressure to deliver the desired flow rate.
  • Material of construction – selecting the right construction material can impact the pump’s longevity. Stainless steel pumps are typically preferred for their corrosion resistance and durability.
  • Noise level – some pumps can be noisy, which can be a nuisance. Ensure that you select a pump that operates smoothly and quietly.
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Popular Pump Models

Now that you know the factors to consider when choosing a pump for your tankless water heater, you may be wondering which pumps are popular in the market. Here are some of the most popular pumps that you can consider:

  • Grundfos comfort pm: This pump is well known for its high head pressure and flexible installation options.
  • Bacoeng: This pump is a popular option for rv owners who require a compact and quiet pump.
  • Laing lhb08100092 autocirc: This pump is designed to be energy efficient, making it an excellent choice for homeowners concerned about their energy consumption.

Selecting the right pump is crucial in maintaining a consistent flow rate and ensuring optimal functionality of your tankless water heater. Consider the factors we’ve discussed when selecting a pump, and choose a model that will meet your specific needs.

Flushing Your Tankless Water Heater With A Pump

Tankless water heaters are an excellent choice to provide hot water efficiently. However, like every other appliance, it can accumulate minerals and sediment build-up in the system over time, leading to clogs and blockages. To prevent these issues and maintain the unit’s longevity, flushing it regularly is necessary.

In this section, we will guide you through the process of flushing your tankless water heater with a pump.

Step-By-Step Guide To Flushing Your Tankless Water Heater

Flushing your tankless water heater may sound like a complicated process, but it’s simple if you follow the right steps. Let’s take a look at the step-by-step guide to flush the tankless water heater with a pump:

  • Turn off the water supply and gas.
  • Close all the water valves.
  • Create a connection between the cold and hot water flush ports using a submersible pump.
  • Make another connection between the pump and water supply.
  • Open hot and cold valves and power on the pump.
  • Let the water flow in and out of the unit, by flushing the system for about 45 minutes.
  • After 45 minutes, switch off the pump and power down the system.
  • Disconnect the pump and the valves.
  • Use a clean cloth to wipe and dry each valve and connection.
  • Turn the valves on and power the system back up.
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Best Practices And Tips For Flushing Your Tankless Water Heater

Flushing your tankless water heater isn’t something you do every day. It’s something that only happens occasionally, and when you do it, you must do it right. Here are some best practices and tips to make the flushing process as effective as possible:

  • Follow the manufacturer’s instructions to avoid any conflicts. Refer to the manual for specific flushing instructions.
  • Flush the system using white vinegar or a descaling solution to remove sediment and mineral buildup completely.
  • Use a submersible pump to flush the system instead of a bucket as it’s more convenient.
  • Be cautious when handling the pump, as it can be dangerous if not handled correctly.
  • Use safety equipment, including gloves and eye protection.
  • Keep the temperature between 90°f and 95°f during flushing, to avoid overworking the pump.
  • Do not reuse the flushed water. Dispose of it safely and responsibly.
  • Keep in mind that fluctuations in water pressure can affect the flushing process. If you’re experiencing fluctuation, contact a professional as soon as possible.

Flushing your tankless water heater isn’t a complicated process. By following the step-by-step instructions and best practices mentioned in this guide, you can easily perform the process in a safe and efficient manner. Remember, regular maintenance is necessary to prevent issues and extend the unit’s longevity.


After reading through this article, we hope you have gained a better understanding of what size pump to use when flushing your tankless water heater. Keep in mind that it’s crucial to follow the manufacturer’s guidelines and instructions for both your tankless water heater and pump.

By doing this, you can prevent damage to your system and ensure its longevity and efficiency. Remember to prepare beforehand, gather the necessary materials, and follow the correct flushing process. Flushing your tankless water heater is an essential maintenance task that can ultimately save you money in the long run by preventing costly repairs.

So, take care of your system, and it’ll take care of you.


I am a mechanical engineer and love doing research on different home and outdoor heating options. When I am not working, I love spending time with my family and friends. I also enjoy blogging about my findings and helping others to find the best heating options for their needs.