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7 Step Guide – How to Flush Tankless Water Heaters.

Tankless Water Heater Flushing: Everything You Need to Know

Tankless Water Heaters are the present and future of water heating. Period. With advances in tankless water heating technology making them fit for every application regardless of its size, tank-style water heaters are rightfully on their way out. However, it is imperative to be aware of the maintenance requirements of tankless water heaters so that you can get the most out of this efficient form of water heating. Flushing is one of the most frequent and critical maintenance needs for most tankless water heaters. This guide will answer any questions that you may have about tankless water heating. How to flush a tankless water heater? How often is flushing a tankless water heater necessary?

After answering these questions, we will look at what makes Intellihot products different when it comes to flushing tankless water heaters. 

Table of Contents

What is Tankless Water Heater Flushing?

Flushing is a routine water heater maintenance procedure to remove the buildup of sediments due to hard water scaling from the water heater's pipes and internal fixtures.

Flushing a tankless water heater is integral to its long-term maintenance. It is a necessary step for most tankless water heaters for a variety of reasons. The single operating principle that makes tankless water heater flushing necessary is scaling.

Scaling is the buildup of minerals from hard water in pipes and other surfaces. You must have observed this buildup on external surfaces like taps too – usually, a white and granular buildup (like the picture attached here). 

Scale buildup on a tap

No matter where you live, the water that enters your property has various levels of impurities or other components. This includes minerals like calcium carbonate which naturally occur in the water present in our planet’s aquatic resources. To clarify, water treatment does not completely eliminate such minerals as these are not technically unsafe for human consumption.

As water runs through pipes and other fittings, these minerals get deposited to their surfaces little by little. Imagine passing coffee through a filter multiple times. Over time, you would find that tiny coffee grounds would accumulate on the surfaces of the filter and little by little, turn into a significant and visible masses. In the case of scaling, the tiny molecules of minerals that get attached to the pipes grow in number and become sizable masses over time.

As the above happens, the area through which the water can pass in the pipes reduces. The scale that deposits in the pipe starts to take up more and more of the surface area within the pipes. Flushing is the periodic procedure of removing the buildup of sediments arising due to hard water scaling in water fixtures.

Why is Tankless Water Heater Flushing Necessary?​​

Flushing tankless water heaters is necessary to:

  • Allow water to move freely and quickly in your water heater system.
  • Maintain the required hot water demand: There will be lesser hot water exiting your tankless water heater system per minute if scaling is reducing the area through which the water can move. Flushing ensures that enough hot water can exit your system and meet the demand calculated while sizing your project.
  • Decrease wait times for hot water delivery: Since scaling clogs pipes as explained above, it would reduce the speed with which water moves through your water heating system. Flushing ensures that there is no reduction in the speed of water movement by removing scale and thereby, decreasing the wait times for hot water delivery.
  • Maintain energy efficiency of your tankless water heater: When there is scale buildup in your tankless water heater, it will consume more energy to heat every gallon of water. For instance, let’s say your tankless water heater moves 2 gallons of water every minute. If scaling blocks 50% of your pipes, only one gallon of water would move through your water heating system every minute. If you run your tankless water heater for 10 minutes, then it would move 10 gallons of water with scale. However, if flushed, it would move 20 gallons in that timeframe. Hence, flushing can help maintain the energy efficiency of your tankless water heater by ensuring the maximum amount of water moves through it. Moreover, scaling will also reduce the rate at which heat is transferred between the heating element and the water. Hence, more energy will be needed to heat the same amount of water with scale buildup.
Water Heater Temperature Costs

Do All Tankless Water Heaters Need to be Flushed?

You might wonder if every tankless water heater needs to be flushed. Every model of tankless water heater is different. Moreover, there is a wide range of the amount of minerals in water in every region on the planet. Hence, the rate of scaling differs due to various factors. However, some form of scale is still present, no matter where you are located or which model of tankless water heater you currently use.

Hence, flushing is a necessary process for almost all tankless water heaters. However, some models work differently. For instance, Intellihot’s tankless water heaters are specially designed to mitigate scale buildup. This means that our products are highly resistant to scaling since they are built with the customer’s ease of operation in mind. Hence, their design provides an easy-maintenance setup with no flushing requirements. You can read more about this below.

What Happens If I Do Not Flush My Tankless Water Heater?

It is not advisable to skip flushing your tankless water heater. It will surely result in unsavory consequences. If you do not flush your tankless water heater, you may encounter the following problems:

  • Lack of hot water: Intense scale buildup can result in incredibly slow movement of hot water. This means that there could be an extremely low amount of hot water exiting the tankless water heater. This amount would then get used up quickly and the slow delivery would not be able to match the demand, resulting in lack of hot water.
  • High wait times: If a tankless water heater is not flushed, the slower movement of water due to scale buildup would mean that you would have to wait much longer for hot water to be delivered.
  • High energy bills: Not flushing a tankless water heater can result in the necessity to operate your tankless water heater for a longer time due to the lower amount of water moving through it because of scale buildup. Moreover, scale buildup will also heighten the energy needed by the heating element to heat the same amount of water. This will cause a decrease in your water heater’s efficiency and dramatically increase your energy bills.
  • Breakdown of your tankless water heater leading to costly repairs: Sediments that get built up due to scaling can also travel to the dip tubes or other essential components of your water heater. This can result in some of these essential elements suffering blockages or breakdowns. Such events can break down the entire unit and force you to undertake expensive repairs.
  • Low Water Pressure: As mentioned, scaling will decrease the speed with which water moves through the tankless water heater. Hence, this would decrease the pressure of hot water outlets. This can result in unpleasant experiences like a shower with lower water pressure.

How Often Do I Need to Flush My Tankless Water Heater?

It is a commonly accepted understanding that you should flush your tankless water heater at least once a year. Doing so more than once is advisable to continue operating it at the highest standards. This is especially true if you live in an area with relatively harder water (that is, water with more mineral sediments). You can check your area’s water hardness using this tool.

USA Water Hardness Map

Can I Flush My Tankless Water Heater Myself? Do I Need a Plumber?

Flushing a tankless water heater is by no means a challenging task. If you possess an adequate amount of working knowledge, you can do so yourself, without the help of a plumber. However, you should make it a point to be fully knowledgeable about the process of flushing your tankless water heater. There might be subtle differences in the procedure based on your particular tankless water heater model.

Hence, we recommend doing your research before attempting to flush your tankless water heater yourself. Read your tankless water heater’s manual, watch a few videos and read a few articles before flushing. 

If you are unsure, it might be advisable to contact a local plumber to do it for you. This could be especially beneficial during the first few occasions. You can observe your plumber flushing your tankless water heater a few times and then choose to do it yourself the next time.

DIY Tankless Flushing Procedure

Flushing most tankless water heaters involves a standard procedure. However, there are subtle differences for each model. It is advisable to refer to your tankless water heater model’s operational manual so that you are fully aware of the process.

What Do I Need to Flush a Tankless Water Heater?

To flush a tankless water heater, you will need the following items:

  • A basic toolkit: To unscrew and screw the necessary pipes and components of your tankless water heater
  • Two hoses: two adequately long hoses that can be connected to your tankless water heater’s cold-water inlet and hot water outlet. Make sure you know the correct type of pipe that can be attached to your tankless water heater’s inlet and outlet. A length of 6 feet is ideal for the hoses.
  • A descaling/cleaning agent: You would need an adequate quantity of a descaling agent liquid that will break down and eliminate the scale in your tankless water heater. The amount needed depends on the size of your tankless water heater and the kind of descaling agent that you use. It is best to refer to your tankless water heater’s manual and instructions of the descaling agent that you choose.
  • A submersible circulation pump: You would need a submersible pump to help the descaling agent flow through your tankless water heater. Ideally, this pump should have a horsepower of 1/5 hp or 1/6 hp. A pump with a higher horsepower would move the descaling agent too fast for it to have an adequate cleansing effect. Again, it is best to refer to your water heater’s manual and the descaling agent’s instructions.
  • A bucket: You would need a big enough bucket to hold the descaling agent and the submersible pump. This bucket should be made out of a material that would not get damaged by the descaling agent. In most cases, a 5 gallon plastic bucket should suffice.
Submersible Circulation Pump


Optional: A Tankless Water Heater Flush Kit

  • Instead of purchasing these items separately, you can also choose to buy a tankless water heater flushing kit. Usually, they consist of all of the above components and will work on most standard tankless water heaters

How to Flush a Tankless Water Heater? A 7-Step Guide

Now that you know the items you need to buy for flushing a tankless water heater, let’s look at how you can use these. It is best to read the operational manual of your tankless water heater to understand the specific procedure. However, this is what the general process looks like:

  1. Turn off your tankless water heating system: First, you should ensure that your tankless water is turned off. Hence, you would need to turn off the gas valve if you have a gas-powered water heater. Followed by that, you would need to turn off your tankless water heater’s inlet and outlet valves. This will ensure that there is no water flowing through your tankless water heater while you carry out the flushing procedure.
  2. Drain your tankless water heater: After shutting off the inlets, you should drain your tankless water heater so that any residual water in the system is ejected. Usually, this involves removing the drain caps on the hot water outlet and the cold-water inlet, followed by collecting the drained water in a bucket. You can drain the inlet and outlet one by one and use the same bucket to collect the residual water that drains.
    Caution: Please ensure that you exercise safety precautions while draining the hot water outlet to avoid burning yourself. For instance, you can choose to wear rubber gloves.
  3. Cleaning the filter: Your tankless water heater might have a prefilter which is located at the bottom of the unit. If this is the case, you would need to wash it to remove any scale buildup. Refer to your water heater’s manual for additional instructions.
  4. Attach the hoses: Attach one end of your first hose to your water heater’s inlet valve and the other end to the submersible circulation pump. Place the circulation pump in the bucket. Attach one end of your second hose to your water heater’s outlet valve and leave the other end in your bucket.
  5. Add the descaling agent and begin the process: Add enough descaling agent to the bucket. Refer to the descaling agent’s instructions and your water heater manual for the adequate quantity needed. Make sure the inlet and outlet valves of your tankless water heater are open and start the recirculation pump. Let it run for the time indicated on the descaling agent’s instructions. It is usually between 45 minutes to a couple of hours.
  6. The end of flushing: After the pump has run for the required amount of time, you can turn it off. You have now adequately flushed your water heater to eliminate any scale buildup. Turn off the inlet and outlet valves and disconnect both the hoses. Remove the pump from the bucket. Empty the contents of the bucket. You can gently clean the hoses, the bucket and the pump and re-use them for flushing later.
  7. Restart your water heater: Now that the flushing is complete, you will need to reconnect your tankless water heater. Connect your inlet and outlet water pipes to the cold water inlet and the hot water outlet respectively. Put the drain caps back on. Turn on your gas line. Let any cold-water outlet in your property run for a few minutes so any excess descaling agent is eliminated. After doing that, your tankless water heater should be ready to go. You can test it by turning on a hot water outlet.

If you are facing any issues with your water heater after the flushing procedure is complete, you should contact your plumber immediately.

What If I Don't Have A Descaling Agent? Can I Use Vinegar to Flush my Tankless Water Heater?

In most cases, you can also choose to use food-grade vinegar to flush most tankless water heaters. Again, it is best to refer to your tankless water heater’s manual to be fully sure. If you use vinegar, be sure to let the pump run for 1.5-2 hours.

How Much Does it Cost to Flush a Tankless Water Heater?

If you hire a plumber, you will probably have to pay anywhere between $100 to $600 to get your tankless water heater flushed. However, if you choose to do it yourself, the cost depends on the equipment you need. If this is your first time flushing a tankless water heater, you would need to buy all the gear mentioned. Here is an average range of the cost of these items on Amazon as of 2023 (each of these items also have more premium and expensive options that can be above the range mentioned):

Hose: $16-$25 * 2

Descaling Agent: $20-$60 based on quantity

Submersible circulation pump: $40-$60

5-gallon Plastic Bucket: $10-$15

Based on the costs above, you can expect to spend $102-$185 to get the gear to flush your tankless water heater for the first time. However, you can reuse the circulation pump, bucket, and hoses. Hence, for every additional flushing instance, you would only need to spend $20-$60 for the descaling agent.

Please note that these prices were obtained from Amazon using a set of standard assumptions. This range can vary for your use case.

Optional: If you opt for a tankless water heater flushing kit, you can get one for $110-$200 with more expensive, premium options available.

Do Intellihot Tankless Water Heaters Need to be Flushed Regularly?

Short answer: No, Intellihot units are designed to handle 2-3 times the amount of scaling than competing water heaters and as a result, they do not need to be flushed.

Intellihot’s innovation-first approach means that we design our products with the end consumer in mind. After reading this article and/or having used a tankless water heater in the past, it is easy to tell that the process of flushing is a routine maintenance headache. The process of flushing usually results in downtime if a property does not have a backup water heating system. Downtime/lack of hot water, even for an hour, can have a significant negative impact for properties like hotels and restaurants. Moreover, if a non-Intellihot tankless water heater is not flushed on time, it can lead to breakdowns, costly repairs, and higher energy bills. Most tankless water heaters that do not have remote access capabilities (unlike Intellihot units) leave the task of scheduling timely flushing to the facility manager.

For instance, the maximum allowable hardness for incoming water at 60 psi and a temperature set point of 120-139 degrees Fahrenheit for Intellihot units is 20 grains per gallon. This means that Intellihot units will resist scaling and continue to function efficiently without the need for flushing if the hardness of water is under 20 grains per gallon. This number is 2-3 times bigger than competing tankless water heaters. That is, most competing tankless water heaters can only handle hardness of 6.66-10 grains per gallon.

Intellihot can achieve this due to its patented heat exchanger which vibrates constantly when in use to resist the accumulation of scaling. Moreover, the ability of Intellihot units to move water at lightning-fast speeds within the system ensures that efficiency is not compromised even if there is some level of scaling. Hence, you do not need to flush Intellihot units regularly on an annual basis.

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