Standard Gas Hot Water Header

DIY: Flush Your Water Heater and Check/Replace Your Anode 38

Flush Your Hot Water HeaterI’m not proud to admit that this DIY project is something I put off for way too long, and I feel stupid because it’s one of the easiest things you can do to save money every month, while prolonging the life of your gas or electric water heater: flushing the tank and inspecting (and replacing, as needed) your sacrificial anode.

“What’s an anode,” you ask? Don’t feel bad, I didn’t know either. And I promise I’ll get there… but first, let me explain what caused me to start looking at my  water heaters in the first place: icky rust-colored water.

Rust Against the Machine

Rust in your hot water is a common occurrence. Nearly all hot water tanks are made out of steel, and everyone knows that if you allow water to stay in contact with steel long enough, steel will rust. Most water heaters are coated on the inside with a layer of porcelain enamel to help slow down the corrosion, but even that interior lining will eventually wear down and allow the steel to corrode. As the steel corrodes, it flakes off and settles at the bottom of your hot water tank, and then eventually breaks down further into fine particles of rusty sediment.

Standard Gas Hot Water Heater

The above cutaway diagram shows the basic parts of a standard gas water heater. If you have an electric water heater (like we have at our cabin because there’s no natural gas out there), it’s very similar, except instead of a gas burner and burner control valve, you’ll have an electric element near the bottom and no exhaust flue on top.

The first problem with sediment on the bottom of your hot water tank is that it will act as an insulating barrier between the flame and the water, meaning you’ll burn way more gas (and spend way more money) every day to heat the water in your tank. The thicker the sediment layer, the less efficient the tank.

However, most people never realize they’ve got a thick layer of rusty sediment sitting at the bottom of their water heater until it builds up high enough to touch, or get close to touching, the end of the dip tube (shown in blue in the above image) where cold water comes into the tank and sends rusty particulate swirling around the tank, where it gets sucked into the hot water tube at the top of the tank (shown in red above), which causes rusty water to come out of your faucet or shower head. Eww.

If that happens, or if you want to prevent it from happening, you need to flush your water heater.

Flush it Out, Push it Out, Waaaaay Out!

As a preventative maintenance step, you should flush your water heater at least once a year, or even every six months. Don’t worry, it’s easy. So easy, you’ll kick yourself for not doing it sooner.

  1. Turn the gas burner knob on your water heater all the way down to the “Vacation” setting. This will prevent the burner from coming on while you drain the tank.
  2. Turn off the cold water shutoff valve that feeds water into your tank. You don’t need to shut off your house’s main water valve.
  3. Connect a standard hose to the drain valve at the bottom of your hot water tank. You can use your garden hose, but I recommend buying a shorter hose from a home improvement store just for this purpose, and then storing it in the same room as the water tank. You’ll need the far end of the hose to be at a lower elevation than the drain valve. If you have a drain in the floor of the room where your hot water tank lives, that’s the ideal spot to put the hose. I generally remove the drain cover and shove the hose down into the drain.
  4. If you have a recirculating pump for your hot water line, turn it off, and close the valve that feeds back into the water tank. If you don’t have one, skip this step.
  5. Slowly open the drain valve until it’s all the way open. Be careful, the water inside the tank is hot. You should hear water draining from the tank and down the drain, or outside, or into the bathtub, or wherever else you put the other end of the hose. Warning: you may be shocked at how much gunk was in the bottom of your water heater. But take comfort in knowing you’re fixing it now, and will never let it get that bad again. 🙂
  6. Turn on (all the way) the hot water tap at a sink that’s closest to your tank and leave it open. This prevents a vacuum from forming and allows the tank to drain more quickly and fully. Water should stop coming out of the faucet within a minute, but keep the tap open.
  7. Once the tank is mostly drained (you can tell when the drain hose has just a trickle of water), turn the cold water valve back on while leaving the drain valve open. You’ll see (or hear) water coming out the drain hose again. Let it flush for a minute or two, then close the drain valve.
  8. Let the cold water refill your tank for a couple of minutes, then shut off the cold water valve again and open the drain tube. Repeat steps 7 and 8 a few times, filling and draining, until the water coming out of your drain hose is clear.
  9. After at least 3-4 flushing cycles, close the drain valve, remove the hose, and make sure your cold water valve at the top of the tank is open, allowing the tank to fill completely.
  10. Turn the temperature setting on your gas valve back to your normal setting, and re-enable your recirculating pump and valve (if you have one).
  11. When the hot water faucet you opened in step 6 starts flowing normally again, you can turn it off. You should also go to every hot water fixture in the house and turn them on for a few seconds to allow all the air in the hot water lines to blow out.
  12. You’re flushed!

You Thought I Forgot The Anode

I promise, I didn’t! We already discussed the fact that most hot water tanks are made out of steel, and that the basic chemical formula of steel plus water equals rust. So, in many water heaters, a long metal stick made of aluminum, or magnesium, or zinc, or some combination of those metals, is inserted from the top of the water heater down into the tank. That rod is a sacrificial anode, and it works using a chemical reaction called electrolysis, allowing the anode to corrode (on purpose) instead of the steel inside the tank. Electrolysis occurs any time two different types of metals are touching under water: the least “noble” metal (meaning the more reactive one) will always corrode before the more noble metal will. And because aluminum, magnesium, and zinc are all less noble than steel, they make great anodes.

Anode rods are relatively cheap. I buy them for around $25 online or at plumbing supply stores, which is way cheaper than prematurely replacing your water heater. They’re designed to be replaced on a regular basis. Exactly how regular depends on a number of factors: how hard your water is, how often you use hot water, whether you use a water softener, the quality of your tank’s internal lining, and a number of other factors.

From time to time, you should inspect your anode to see how corroded it is, and whether or not it needs to be replaced. A great time to remove your anode for inspection is while you’re flushing your water heater. Make sure the cold water valve is turned off, and that at least some of the water is drained from your tank so that water doesn’t spill out the top of your tank when the anode is removed.

There are two types of anode rod designs: standalone anodes and anodes that are integrated with your tank’s hot water tube. Both require slightly different procedures to remove, inspect, and replace.

A standalone anode has a 1 1/16″ (that’s one and one-sixteenth inch) hexagonal head on top and a threaded collar underneath. Here’s what a new one looks like, next to one that’s corroded to the point that it needs replacement:

New Anode and Corroded Anode

New Anode and Corroded Anode

If you have a standalone anode in your hot water tank (like we do at our Seattle house), you should be able to see the hexagonal head on top of the tank (unless it’s under some sort of access cover). With the tank partially drained and the cold water valve turned off, use a 1 1/16″ socket to loosen the anode.

Fair warning: if your hot water tank is a few years old, and you’ve never removed the anode, it’s probably rusted in tight and will be WAY harder to remove than it sounds. The manufacture date shown on the side of my water heater was 1996, and I didn’t even realize my water heater had an anode until 2012, so I had to go to extreme measures to remove mine, like spraying it with anti-seize bolt loosener (available at most auto parts stores) and asking my 300lb Icelandic power-lifter and black belt karate buddy Axel Adalsteinsson to supply the muscle with a cheater bar. You might also consider using an impact wrench if you don’t have an Icelandic buddy handy.

If you can’t find an anode on top of your hot water tank, you may have an anode that’s integrated with the tube that pulls hot water from your tank. The hot water tanks at our Utah vacation house have integrated anodes, and here’s what they looked like when I last removed them:

Integrated anode connected to hot water outlet

Integrated anode connected to hot water outlet

To remove an integrated anode from your tank, it’s best to have two pairs of channel-lock pliers or plumber’s wrenches. With the tank partially drained and the cold water valve off, use one wrench to hold the anode in place while you loosen the hot water line with the other wrench. Once the hot water line is removed (have a towel handy, it will drain a bit), gently grip the non-threaded portion of the exposed collar and turn counter-clockwise to loosen where the anode is threaded into the tank.

With either type of anode, once you’ve got it free, pull it up out of the tank and and inspect it. If it’s heavily corroded (as shown in both examples above), pull it all the way out. If you can see any part of the steel wire core on your anode, it needs to be replaced. If it’s just slightly chewed up, then you’re fine to keep it in there, and check it again in six months (set a reminder in your phone or calendar).

If it needs to be replaced, take the old anode with you to a plumbing supply or hardware store so you can get the right size replacement, or measure it and order one online. A few inches shorter or longer than the original isn’t a big deal, and if you can only buy one that’s too long to fit in your tank, a hacksaw can solve that problem fairly quickly. I keep a spare anode next to each water heater, so that when I inspect the old one and discover it’s time to replace it, I can install the spare right away, then purchase a new spare later.

When installing an anode, I recommend using plumber’s teflon tape to help ensure a tight seal, prevent rust, and make removing for inspection every six months far easier.

The Metal! (Yes, I’m a Tenacious D fan)

What type of metal you should choose for your anode depends on the water in your area.

  • In most cases, the magnesium anode rods are preferable over the aluminum ones, as they will last longer than aluminum ones. In general, the magnesium rods will have a small “bump” on the top, while the aluminum ones have a flat top.
  • If you have extremely hard water, aluminum anode rods are often your best choice. Magnesium anode will only last 1 or 2 years  against really hard water.
  • So called “zinc” anode rods are actually just aluminum rods with about 10% zinc mixed, which helps fight sulfur smells in your hot water. They’re slightly more expensive than magnesium or aluminum rods, but are worth the upgrade come replacement time if your hot water smells like rotten eggs.

You can experiment with the different types over a few years to see which metal work best for you.

Congratulations… You’re a Plumber!

OK, so maybe you’re not quite ready to hang out with Mario and Luigi professionally just yet, but just knowing that your water heater has a user-replaceable anode is more than most people. Regular flushes of your hot water tank and inspection/replacement of your anode can extend the life of your water heater by years… if not decades, and save significant money every month by lowering the amount of energy required to heat the water in your tank.

So instead of waiting (like I did) until you actually see rust in your water, be proactive with a 6-month schedule of flushing your tanks and inspecting your anodes. I also recommend attaching a written log to your water tank, or use an online Google spreadsheet, to track how often you flush and inspect/replace the anode. Happy flushing!

Oh, and if you ever need a 300lb Icelandic power-lifter black belt to remove a rusted anode, sing a Viking ballad, or scare the women and children in your village, I know one that makes house calls.

Steve and Axel

My anode-busting buddy Axel, hanging out with me at a karate conference in Atlanta

Further Reading:

I found this great technical document from Rheem/Ruud, which goes into even more detail about anodes and why they’re essential for your water heater. There’s some good stuff in there, including some interesting photos.

  • Mike Craft

    Thanks for the excellent post Steve, one of the MANY things I am sure I am supposed to be doing to take care of my homes that I have never even heard of! Our hot water stinks, and takes forever to heat up a new batch once it runs out (if the wife and daughter take a shower in the same day that’s all it takes, only 50 gallons…). Something to add to my list to do to make me feel more manly and independent :D.

    • Thanks, Mike. I didn’t include this in the main article, but if you really want to speed up the draining steps (which is usually what takes the longest) you can use a small pump that uses garden hose hookups. I bought a Simer M40P on eBay for $35, which turbocharges the flushing process.

      • Mike Craft

        ROck-on, thanks for the tip, always looking for an excuse to buy a new tool, and anything to save time is worth every penny! THis one will certainly pay for itself vs. having a plumber do it or worse having to buy a new water heater!

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  • Funky Monk

    Hope you don’t mind a contrarian option..

    If you are consistent with flushing, (every six months), it is not necessary to turn off the water supply, and you only need to flush for ten to fifteen seconds. Anything more is overkill, and wasteful of water and energy.

    That’s my experience, anyway.

    • Thanks, Monk. Excellent point, and I totally agree. Once your tank is flushed, a mini-flush twice a year should be fine. But if it’s been a while and icky stuff is coming from your tank, best to do the full Monty. 🙂

  • Mark

    Thanks for the blog Steve. I found it to be very helpful.

    We had been getting alarms on the intelivent controller for our HWT (2006 new) so after scouring for info we came to the conclusion that the corrosion anode needed changing.
    After much running around trying to find a 1-1/16 socket (biggest I had was 7/8) then having to find a 1/2 drive wrench (FYI I found out I have 3, 3/8 drive sets if anyone needs) I finally managed to loosen the anode, without needing a 300lb Icelandic power lifter.

    The anode itself was partially corroded away but not nearly as bad as I thought it was going to be.


    • Hey, Mark. I did the same scrambling around for a 1-1/16 socket (auto parts store did the trick), and I also believe I have a similar collection of 3/8 drive sets. 🙂

      Did you swap out the anode anyway? And did that silence the alarms?

      • Mark

        Yes i did swap it out, and flushed the tank a couple times too.
        Filled the tank back up and now waiting on heater to finish heating water, then we play the waiting game to see if the alarm comes back up.

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  • Martin

    Excellent info. I’ve been changing anodes for 15 years but too lazy to flush the tank. But you’ve inspired me to do that this time. And good tip from Funky Monk about quick flush once known to be pretty clean.
    I believe you need to go easy with the Teflon tape. There needs to be some metal to metal contact to provide an electrical connection. The rods I buy are pre-taped so I don’t add any extra. Perhaps someone can confirm?

    • Hey, Martin. That’s a good question. However, I still recommend plenty of Teflon tape, because the threads of the anode don’t need to touch the tank in order for it to work properly. In fact, most anode mounting threads (on the female side) will have a plastic insulator between them and the tank, meaning even without any tape, the male threads of the anode still wouldn’t be making contact with the sides of the tank! As long as the anode is dipped in the water, it will work. Therefore, I use a generous amount of Teflon tape, which not only helps ensure a tight seal, but hinders corrosion on the anode’s threads so it’s easier to periodically remove it and see how it’s holding up.

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  • chuck herman

    This is about the best set of instructions for anything that I’ve ever seen. And away we go…..

  • Dale Speckman

    Thanks. Ready to tackle my first flush!

  • Alicia

    I live in Kirkland, Wa and I noticed that my water when running my bath was rusty colored..typed in what causes it and your article came up…very helpful..will definitely try…once I get over my fear of working with gas…haha…I’m really glad to see that its hopefully not my pipes and its an easy fix

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  • Brian

    I love coming to a blog like this and getting perfeclty detailed instructions like you have provided. Thank you for putting the time into providing these details. You can’t go wrong following your step by step instructions. THANKS!

  • Pierre

    Hi Steve,

    Very good article, did flush my tank a couple of weeks ago and sure needed it. I had to flush the system numerous times before the water coming out at the other end came out clean. I guess the previous owner never bothered doing that! Never managed to unscrew the anode though and I don’t have a 300 lbs icelandic friend to do the job! The problem I have still is that the water is still somewhat rusty in colour and I was hoping that the remaining sediments, that is probably still in the water, would fall to the bottom eventually. Does it take a while after you have flushed the system for the the water to completely clear out? Thanks

  • Pierre

    Hi Steve,

    I flushed my tank as per the above instruction and got a lot of rusty debris out. After numerous flushes, the water seemed clean, but it appears to have the same rusty color in my hot water when i fill up the tub. Do you have any additional tips?

    Thanks again


    • Hi, Pierre. That means there’s still a source of rust somewhere. It’s possible that there is a rusty spot on the interior wall of your tank (which would be bad), or it might also mean that there is an iron fitting somewhere inline to your tub. Is the tub the only place that sees the rusty water? If so, then try to locate the iron fitting (probably near the tap). If it’s all over the house, and multiple flushes doesn’t fix the issue, it’s probably time for a new tank.

      • Pierre

        Unfortunately the water is rusty all over the house! For one I was never able to unscrew the anode (don’t have a 300 lbs icelandic friend!) so can’t really see if this could also contribute to the problem. The previous owner mentionned that he acquired that tank in 2007, but who says that the owner before him actually wasn’t renting that tank until he acquired it, meaning paid the remaining balance in 2007. There must be a spot on the tank where one can actually find out when the tank was constructed, right? I was hoping after I flushed the tank that the rusty color cause by the suspended sediments would settle after a while, but that was two weeks ago. I may give it a second set of flushes this weekend and see what happens. If this doesn’t do anything, indeed may it is time for a new tank! 🙁

        Love your blog btw

        Thanks again


        • Darn, Pierre. If you can’t check it, but it’s been in there a while, then there’s a strong possibility that the anode is all gone and corrosion is in your tank. But don’t worry — you can replace it yourself!

          Also, there should be a sticker on the water heater with a model number. The year of manufacture will be part of the model number.

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  • Arthur

    This is great info. Steve, you said this but I think one of the “magnesiums” should be “aluminum”:
    the magnesium rods will have a small “bump” on the top, while the magnesium ones have a flat top.

    • DERP! Thanks for the typo catch. I’ve fixed it. The magnesium rods have the bump, the aluminum ones are flat! 🙂

  • EJ Figueras

    Question…isn’t it potentially dangerous to do this? Couldn’t the tank eventually rust through resulting in a leak?

    • Hi, EJ. Flushing the tank and checking/replacing your anode is not dangerous at all (provided you take proper precautions, shut off the water, and are careful not to scald yourself in the process). If you neglect your water heater, it will rust through and leak prematurely. If you take care of it (including flushing), you’ll get many more years of life from it.

  • If it’s yellow, that could be sulfur. You can purchase test strips from most home improvement stores, and test to see if it shows positive for lots of sulfur. It’s also possible that it’s rust in iron pipes or the hot water tank, which appears kind of yellow when diluted with the water. If it’s rust, that’s from your plumbing (pipes or tank) and the water color generally clears up after you’ve run it for a while. If it stays yellow, even after a long while, that’s probably sulfur in the water source. If you’re drinking the water, you should be testing it at least annually. There are services online where you can send a water sample and they do a full analysis for safety and content. If you’ve never done that… I would. But the DIY strips can be a quick way to see if you can find sulfur, iron, etc. in your system.

  • Carol Sandoval

    I had a plumber come to my house 10 years ago from Home Depot and put my water heater outside in my garage .he used all brand new pipes . I never had a rust taste in my water before.Now a new plummber said i needed a new water heater just put it in about 3 weeks ago all the sudden i have bad rust tast in my water . all my plumbing in my house looks like corrosion all over the fixtures. where as i just check all the fixtures,because i had a leak outside my house and the City ask me to check for leaks so i did and nothing was wrong with my plumbing. I am so confused on what happen .Can anyone help me on what to do . Thank you

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    I just found your blog while desperately trying to figure out how to get rid of the NASTY egg smell in my water. Of course, we are on a well and have all the koodies that go with it. We had manganese (black water), sort of high Iron (yellow ring in the toilets) and the favorite Hydrogen Sulfates (nasty smelly egg), all at once. OMG, how do you hold your nose and brush your teeth at the same time….not easy. Got an IMS system that works fantastic as long as you are talking about the cold water. BUT, the hot water was NOT cooperating with my sensitive olfactory organ (nose). So, I went searching on the internet for the solution to this disgusting situation and I found YOU! This is my round-about way of saying, Thanks for being here and having a bi-layered answer to my hot water tank problems