How to Flush a Water Heater and Prevent Problems such as Sediment build-up, Noise, and Odors

Is your water heater not performing as well as it used to?

Are you noticing signs of sediment buildup or bad odors?

If so, it might be time to give your water heater some much-needed TLC. One of the best ways to ensure optimal performance and extend the lifespan of your water heater is by flushing it regularly.

Rusty water for a water heater
photo: pixabay

In this article, we’ll show you how to flush a water heater in simple, easy-to-follow steps. This guide will also cover the chlorination process to clean the heater of rotten egg odor, discolored water conditions, and bacteria.

By the end of this guide, you’ll be equipped with the knowledge and tools you need to keep your water heater running at its best. Let’s get started!

How to Flush a Hot Water Heater: Considerations

  1. What’s the purpose of flushing a water heater?
  2. Instructions on how to flush a water heater
  3. How to flush with chlorine
  4. How to flush with hydrogen peroxide

What’s the Purpose of Flushing a Water Heater?

Flushing your water heater is crucial for several reasons.

One of the main reasons to flush a water heater is if your hot water is rusty or brown, which is often a sign of material buildup inside the tank due to rust particles from plumbing, water softener resin, sand, clay sediments, and other earth materials. If your home plumbing is connected to the water mains constructed of steel or cast iron pipes, rust can accumulate in the tank, causing brown or rusty water.

Another important reason to perform flushing is to eliminate the rotten egg smell. This odor is actually a hydrogen sulfide odor caused by bacteria. The only way to control smelly water is by removing the bacteria, which can be achieved through this process.

Water heater flush is also necessary to remove sediment build-up. These mineral deposits are the main causes of slow and inefficient water heating, rumbling, and pounding noise. Using a softener, sediment cleaner, or delimer solution in combination with tank flushing can help prevent mineral buildup.

Regular flushing also extends the life of your water heater by keeping it in good working condition and reducing the risk of breakdowns and malfunctions.

When Is the Best Time to Flush a Water Heater Tank?

If you’re wondering how often you should flush your hot water heater, it’s best to follow the manufacturer’s recommendation, which is typically once every 6 months to one year. However, the frequency of flushing also depends on your local water condition. If your water is hard and contains more minerals, you may need to do it more often.

To maintain your water heater’s performance and efficiency, it’s recommended to drain 1 to 2 gallons from the drain valve every month as a minimum requirement. This helps remove any sediment or debris buildup that may have accumulated in the bottom of the tank. By following these guidelines, you can ensure that your water heater stays in good condition and provides hot water on demand.

How to Flush a Water Heater: A Step-by-Step Guide

Required Tools for the DIY Project

  1. Adjustable pipe wrench
  2. Screwdriver
  3. Hammer
  4. Teflon tape
  5. Garden hose
  6. Shop-Vac
  7. Ball valve
  8. Fittings


Here’s how to flush a water heater in simple steps:

  • If using a gas water heater, turn the gas control valve to the OFF position. You can also close the valve on the gas pipe that supplies the heater.
  • If using the electric heater, turn the electricity OFF on the circuit breaker (breaker box).
  • Turn OFF the cold water supply to the heater on the main shut-off valve (usually installed near the cold water inlet). It can be recognized as the valve with the lever (ball valve) or with the wheel (gate valve).
  • Open a hot water faucet to prevent the vacuum from forming in the heater while draining.
  • Drain the heater by connecting one side of the garden hose to the drain valve, and place the other end to the floor drain or outside. You can speed up the process by opening the TPR valve in the upper part of the unit and placing the bucket under to catch the water.
  • The water should be running from the relief valve, and if not (if it is clogged), replace it with the new one with the same specs. If the purpose of draining is to remove the sediments, drain them until the water runs clear with no debris. If the situation is worse than you expected, you might have to drain it completely.
  • Turn back ON the cold water into the heater.
  • Allow water to run through the heater and out of the drain valve. Flush the heater for five or ten minutes.
  • Close the drain valve and keep the tap open while refilling the tank heater.
  • Once the tank is full of water, open the pressure relief valve to bleed the air.

Next, use the instructions found on the unit’s label to light the pilot, or resume the power. It is essential to have a tank full of water, especially on electric models, because if the heating element is exposed to air, it burns out easily.

How to Flush a Water Heater With Chlorine

Flushing a water heater through the drain valve provided at the bottom of the heater with the appropriate dissolver, like chlorine, is one way to control and eliminate bacteria from the heating system. Below is the proper procedure for chlorinating a heater, recommended by the Bradford White manufacturer:

  • Turn off the water, power, and/or gas supply to the heater.
  • Use the drain valve located at the bottom of your heater and drain several gallons.
  • Remove the anode rod.
  • Pour a 1/2 to 1 gallon of bleach into the tank through the hot water outlet opening.
  • Install the new anode rod or bring the old one back if it is still functional.
  • Re-connect the hot water supply line to the outlet on the heater.
  • Turn on the water supply and draw water to every hot water fixture in your home until the chlorine smell is detected. Keep in mind that all plumbing lines must receive the treatment.
  • Once the chlorine odor is noticed, turn off the faucets and allow the bleach to sit in the heater and plumbing lines for a minimum of 3 hours, a full day is desired.
  • Turn on and draw water at each tap in your home to flush all chlorine from the piping till the odor is no longer present.
  • Turn on the power and/or gas supply to the heater.

Water softeners, long periods of no water movement, or using a well supply are all potential causes of the bacteria’s presence. This is why shock-chlorination of the heating system is recommended. Combine the above process and flush the hot water heater often if you have a heavily infected system.

This is also an opportunity to check out some of the elements such as the anode rod and drain valve. If the anode rod has been consumed and it doesn’t perform as before, replace it.

How to Flush a Water Heater With Hydrogen Peroxide

  • If the water heater is electric, turn the electricity on the breaker box to OFF, and do the same thing if the unit is gas-powered, or simply turn the gas control valve to the pilot position.
  • Open the nearby hot water tap and TPR valve.
  • Drain enough water to provide space for hydrogen peroxide or below the TPR valve level.
  • If the storage tank has a capacity of 40 gallons, add 1-2 pints of 3% hydrogen peroxide. If it is a different size, change the amount accordingly. Pour the peroxide through the opening of the TPR valve, anode rod, or the water outlet if possible.
  • Open the cold water inlet valve to fill the tank and close it.
  • Leave the hydrogen peroxide for a few hours in the tank’s water.
  • Open the cold water valve again and hot water tap so the hydrogen peroxide can flush the supply lines.
  • Drain all the water and peroxide from the tank (including debris).
  • Close the drain valve.
  • Fill the tank with water thoroughly.
  • Repeat flushing through the pipes and drain the water again, if necessary (if, for example, smelly water is still present or water is not clear).
  • Fill the tank with water (the drain valve is closed).
  • Purge the air from the tank with the open hot water faucets. Also, use the pressure relief valve to bleed the air.
  • Resume the power and heating operation.

Note: You can also use vinegar, even apple cider vinegar, for flashing, in the amount of one gallon.

Most water heaters have the plastic drain valve factory-installed, so while flushing the unit, debris can clog the valve and cause leaking due to improper seating. Replace it with the ball valve.


Knowing how to flush a water heater is an essential maintenance task that every homeowner should know. It helps to ensure the longevity and efficiency of the heating system, prevent potential hazards, and provide clean and safe hot water for your household. By following the simple steps outlined above and flushing your water heater regularly, you can avoid costly repairs and replacements while extending the lifespan of your unit.


Is It Better to Flush or Drain a Water Heater?

Flushing and draining a water heater serve different purposes. Draining removes sediment buildup, whereas flushing removes bacteria and mineral deposits. Therefore, it is best to both flush and drain a water heater regularly for optimal performance and longevity. Draining can be done annually, while flushing is recommended twice a year.

Are You Supposed to Flush a Tankless Water Heater?

Yes, tankless water heaters also need to be flushed periodically to remove mineral buildup and debris that can affect their performance and efficiency. The frequency of flushing depends on the hardness of the water and the manufacturer’s recommendation, but typically it is recommended to flush the system every 6-12 months.

Can Flushing a Water Heater Cause Any Damage to My Plumbing System?

No, flushing your water heater is a routine maintenance task that is actually beneficial for your plumbing system. However, if you notice any leaks or other issues during the process, it’s important to address them promptly to prevent damage.

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