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How to flush your water heater. (And what happens if you don't!)

This can help you keep your water heater running in tip-top shape for years to come — and prevent an expensive disaster that involves a late-night or weekend call to a local plumber.

Water heaters are one of the most essential appliances in your home. They’re a big investment, and most of our clients want to make sure they protect their investment for as long as possible. 

Performing annual maintenance on a tank-style water heater by flushing it will extend its lifespan. This can help you keep your water heater running in tip-top shape for years to come — and prevent an expensive disaster that involves a late-night or weekend call to a local plumber. 

Why Should I Flush My Hot Water Heater? 

Flushing your water heater is an easy DIY project and will remove the damaging sediment that can accumulate in the bottom of the tank after prolonged use – and it’s one task that many, many homeowners don’t even know they should consider. Sediment can block or clog your water heater's pressure relief valve and can cause your water heater to lose efficiency. If the pressure relief valve gets blocked, it’s no longer operating as a safe pressure relief outlet, and the safety of the water heater tank is compromised. 

Sediment can also make your water heater less effective by reducing its hot water output over time, making it less energy efficient and costing you money. The sediment sits in the bottom of the tank and gets in the way of the heating system, keeping it from heating efficiently. This is especially true if you have hard water in your home – hard water contains a higher percentage of minerals and debris that can then become sediment in your hot water tank. 

Sediment that accumulates in your tank. (Don't worry! It doesn't come out of your faucets.)

If neither you nor a professional have flushed your water within the last five years, Water Heaters Now recommends not flushing it yourself. If you flush a water heater that already has a significant sediment buildup, it can actually cause more problems. Excessive or large sediment pieces can get stuck in the tank drain valve, or end up exiting the water heater and going through the pipes in your home – and neither of those is an easy fix. Often, if the water heater hasn’t been flushed in a long time then a replacement is necessary if there is no other maintenance solution. If your water heater hasn’t been flushed in a while, give us a call at 612-778-4664 and we’ll be happy to take a look and provide the best next steps to get your home back in optimal shape.

If you are ready to tackle this project yourself, here’s a step-by-step guide to help you flush your hot water heater (and make sure to check out the videos at the bottom of this article!). 

How To Flush Your Hot Water Heater

Step 1: Turn off Gas or Electricity

If you have a gas water heater, turn the gas valve to the "off" position. You can also turn the gas off to the unit at the gas shutoff valve. 

If your water heater is electric, turn the electricity to the water heater off at the circuit breaker. You must turn off an electric water heater completely before flushing or you will risk burning out the heating element.

Step 2: Shut off the Water

Shut off your water heater's water supply. This is the cold water line that goes into the top of your water heater. 

It’s important to wait for the water inside the water heater to cool before flushing as it can remain scalding hot for a long time. You can start this step at night after everyone in your household has no need for hot water.

Step 3: Open a Faucet

Open a hot water faucet somewhere in your house. If you want to drain your water heater faster, a tub faucet likely has the highest flow rate in your home.

Step 4: Connect a Hose to the Drain Valve

For this step, you will need a hose that you will connect to the drain valve on your water heater. Then you will run the hose to a drain, either in your house or outside. A typical garden hose will be sufficient.Make sure the hose is attached securely to the drain valve on the water heater to reduce the chance of spray when you open the valve. 

Step 5: Open the Drain Valve

Now that you have your hose all hooked up and positioned outside or to a floor drain, open the drain valve on your water heater and allow the tank to completely drain. This will likely take 30-40 minutes for a 40-gallon tank water heater.

Step 6: Turn Water Supply Back on and Flush

In order to get the buildup agitated out of the bottom of the water heater tank, you’ll need to flush the water heater with new water from the cold water valve. After the tank is completely empty, turn the cold water supply at the top of the tank back on. Then, allow water to run through the heater and out of the water heater drain valve and hose for approximately 5 to 10 minutes. 

Repeat this process at least 2-3 times to get all the sediment buildup out. You will know your water heater is successfully flushed when the water runs clear out of the end of the hose.

Step 7: Refill the Tank

Now that your water heater is flushed and all the sediment has been removed, it’s time to refill it. Close the drain valve and remove the hose. Then, with the cold water source still on, allow the tank to refill. You will know the tank is full when water begins to come out of the hot water faucet you have left open, even though the water will not be hot. 

Step 8: Turn the Water Heater Back On 

Once it’s full, you’ll need to turn the hot water heater back on so it can be, well… hot! 

With a gas water heater, you’ll need to turn the gas back on to the water heater. Next, you’ll turn the control dial to pilot and click the ignition switch 2-3 times. Check the sight glass to make sure the pilot light is running. On many models, a green light will start flashing to tell you that it’s working. 

You may need to turn the control dial back to the thermostat setting you desire. Consider keeping the heat setting between 120-130 degrees, especially if you have kids in the home. It should keep your water hot enough for showering, but not so hot that the water can scald.  

If you’ve got an electric heater, you’ll need to turn that breaker back on to send power to your electric water heater. Listen at the unit for a low humming noise, and you’ll know it’s back in service. You should have hot water in about 45 minutes. Since you didn’t touch anything with the thermostat when you turned the unit off, it’ll resume the temperature you had it set to before you flushed the water heater. 


That’s it! Now your water heater is successfully flushed and ready to perform at maximum efficiency again. Following these simple steps will help you get the most out of your water heater year after year – just make sure to add it to your maintenance calendar for next year, too. 

If you have any questions about how to perform this maintenance, just give us a call at 612-778-4664. Our expert technicians are standing by, ready to answer your questions. 

Video: How to Flush Your Gas Water Heater 

Here’s Ray demonstrating how to perform annual maintenance on a gas tank-style water heater: 


Video: How to Flush Your Electric Water Heater

Here’s Ray demonstrating how to inspect and flush an electric water heater: 

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