How to Flush a Tankless Water Heater on Your Own in Just 8 Steps
Clear out water heater sediment like a pro
- Rubber gloves
- Inlet (cold) and outlet (hot) water hoses
- Circulation pump
- Channel lock pliers
- 5-gallon bucket
- Tankless water heater flush kit (optional)
- Store-bought water heater cleaner
- Distilled white vinegar (optional)
Maybe you hear some loud knocking and grumbling coming from your water heater, or perhaps you’re just trying to keep up with water heater maintenance. Either way, you need to flush your water heater at least once a year—yes, even tankless water heaters!—to avoid leaks or water heater failure. While you can call in a local tankless water heater company to handle this project, it’s possible for an experienced DIYer to tackle. When you’re ready to check this task off your yearly maintenance to-do list, you can use this step-by-step guide on how to flush a tankless water heater.
Why You Should Flush Your Tankless Water Heater
Many homeowners incorrectly assume that tankless water heaters don’t require flushing; after all, there’s no tank for minerals and sediment to build up. While it’s true that this type of water heater comes with a lower risk of sediment, the internal components in your tankless water heater can still get mineral build-up on them, especially if you live in an area with hard water. This sediment can significantly reduce the efficiency of your appliance, increasing your utility bills and decreasing the lifespan of your water heater. A quick flushing can get rid of any mineral accumulation and get your water heater working like new again.
How Often To Flush Your Water Heater
Since tankless water heaters lack a tank where sediment build-up is a particular problem, you can flush your tankless heater about half as often: once per year. It’s a good idea to flush your tankless water heater in the early fall, as the fixture will work overtime in the cooler weather of the fall and winter, and removing minerals before that time can help keep your heater running for longer.
Shut Off Gas and Isolation Valves
To start, you’ll want to shut off the red and blue isolation valves—red for the hot water and blue for the cold water. Place a bowl or bucket beneath the valves in case any water leaks out. Try to open the valves with your hands, but you can use the channel lock pliers if they give you any trouble. The valves are shut off when they are positioned perpendicular to the pipe and on when the handles run parallel to the pipe.
Shutting off the cold water valve prevents more water from coming into the water heater as you’re cleaning it, while the hot water valve will prevent the distilled white vinegar or other cleaner from flowing from the water heater to your home’s fixtures and appliances.
With these water lines shut off, you’ll also need to shut off the gas line to prevent the water and cleaner from heating up while you’re working. To turn off the gas supply to the water heater, turn the gas valve about 1/4 of a full turn, until it is perpendicular to the supply pipe.
Connect Hoses to the Valves
If the valves have caps, make sure to remove them to attach the water hoses to the isolation valves. Your water heater flushing kit typically includes hoses, or you can use washing machine hoses. Use your pliers to tighten the connections, but be careful not to overtighten. Be firm, but don’t overdo it.
Connect Cold Water Hose to the Circulation Pump
Photo: Vitaliy Halenov / iStock / Getty Images Plus / Getty ImagesOnce you’ve confirmed the hoses are tightly secured to the isolation valves, you’ll connect the other end of the cold water hose to the circulation pump. This device should be included in a tankless water heater flushing kit, or you can purchase it separately. Place the circulation pump into your 5-gallon bucket.
Wondering about the hot water hose? The other end of that will go into the 5-gallon bucket as well.
Add Vinegar or Cleaner
Pour at least two gallons of a 1:1 mixture of water and vinegar or store-bought water heater cleaner into the bucket. The circulation pump should sit completely below the level of the liquid, as should the end of the hot water hose. If not, you risk burning out your pump.
Start Circulating the Water
Open the valves and start the circulation pump to begin flushing the system. For vinegar, let the water and vinegar circulate for one to two hours. For cleaning agent, flush the system based on the time recommended on the label, usually 45 to 90 minutes.
Complete a Final Rinse
Turn off the circulation pump and shut off the water valves as you did at the beginning of the flushing process. Disconnect the hose from the cold water valve, then turn this cold water valve back on. Keep it on for about 10 minutes to rinse away any remaining vinegar or cleaner. Once this process is complete, you can turn the cold water valve back off and disconnect the hot water hose.
Dispose of Excess Cleaner and Minerals
Now, you likely have a bucket of dirty vinegar and sediment on your hands. You can safely dispose of vinegar down a drain or even outside without contaminating community water sources, but if you use a store-bought cleaner, follow the manufacturer’s instructions for disposal. Make sure to rinse out the bucket thoroughly after disposing of the vinegar or commercial cleaner.
Reconnect the Water Heater Valves and Gas
Place the service port caps back over the isolation valves if you had to remove them earlier. Turn on the isolation valves and then the gas supply valve, all of which should now be sitting parallel to the pipes. As a final step, turn on a faucet and let it run for one to five minutes to flush out any possible remaining vinegar or cleaner. Do a quick check for leaks, and then call this project done!
DIY vs. Hiring a Pro
Hiring a water heater professional to flush a tankless water heater costs around $200, so you could save up to $100 by doing it yourself if you already have the necessary tools on hand (tankless water heater flushing kits cost about $100 to $200). However, this isn’t a job to take lightly; if something goes wrong, or if you find a leak, it could cost you over $1,000 in water heater repairs and water damage remediation.
For most homeowners, it’s best to take on simpler things like fixing leaky faucets and opt to hire a water heater repair specialist to flush the tankless water heater quickly and safely. A water heater pro can usually inspect and flush the water heater in under an hour, and they can address any leaks or damage they find on the spot. This could save you hundreds in water damage, not to mention provide some peace of mind that the work will be done properly.
Frequently Asked Questions
There’s no need to pick up commercial chemical solutions at the store for this project, as you can use distilled white vinegar and water to clean the tankless water heater. If you use a store-bought cleaner for water heaters, just make sure you thoroughly circulate the water to rinse away the chemicals. When deciding which option is right for you, consider that a commercial water heater descaler could need about half the time or less to remove sediment and mineral build-up. If you’re tight on time, consider a store-bought water heater cleaning solution.
You should flush a tankless water heater about once per year, which is half as often as you’d go through the process for a standard tank water heater. Although tankless water heaters don’t hold the same water quantity as tank models, and that extra water can lead to more buildup, the flushing process helps clean the water heater and pipes so everything runs efficiently. If you have especially hard water and don’t have a water softener installed, planning to flush your water heater about twice per year might be a better option.
When you don’t regularly flush a water heater, minerals and sediment from your water—namely, magnesium and calcium—can build up inside, which can cause several problems. For one, you’ll start to hear an annoying knocking sound inside the water heater any time you’re using warm or hot water. The buildup can also prevent water from heating up efficiently, or it could cause holes in the pipes or the walls of the water heater over time. Flushing a water heater is an inexpensive way to prolong the life of your appliance and reduce your utility bills in the meantime.
