How to Descale a Tankless Water Heater and Prolong Its Life
Get out the gunk and keep the hot water flowing
- Face mask
- Rubber gloves
- Safety glasses
- Tankless water heater flush kit
- Distilled white vinegar
Almost no one likes a cold shower. Descaling your tankless water heater will help keep it running efficiently and make sure you have hot water any time you need it (or just want it for a relaxing bubble bath). This project will be a breeze if you’re already somewhat familiar with the parts of your tankless water heater, making it perfect for the all-around DIYer. However, hiring a plumber can save you time and give you peace of mind that the job is done properly, especially if you don’t know the difference between the valves on the tank.
When you descale your water heater regularly, you prolong its life span and prevent possible water heater failure. So no matter if you DIY this one or hire a pro, this is definitely an important project.
Some DIY repairs are great for saving money and sharpening your skills, but leave larger jobs like water heater repair to the pros. An experienced hand can ensure the task is completed safely and will prevent further damage.
Prepping to Descale Your Tankless Water Heater
The first step in learning how to descale a tankless water heater is taking care of some prep work.
Buy a Kit
First, you’ll want to go to your favorite home improvement store or website and purchase a tankless water heater flush kit. These typically come with a pump, two hoses, and a big bucket. Most kits cost between $100 and $200, but you may find some kits outside that range. After you get this, you can pop over to your local grocery store and pick up four gallons (roughly 15 liters) of distilled white vinegar.
Grab Safety Equipment
Before you get started with the descaling process itself, you need to get some safety equipment. You’ll be working with vinegar during this process, a notorious archnemesis of the mineral deposits that can build up in your water heater. Though cleaning with vinegar is a very common practice, it can also be irritating and even damaging to your eyes, throat, nose, and skin if you don’t use it properly, according to the National Capital Poison Control Center.
For these reasons, it’s incredibly important that you wear sturdy rubber gloves, a face mask, and eye protection during this process. Food-grade vinegar is typically perfectly safe to handle, but you should always stay on the cautious side. And just as a reminder, NEVER mix vinegar with bleach.
Get Familiar With Your Heater
Finally, you should locate several important valves and water heater components. You’ll see a red isolator valve and a blue isolator valve; red is for hot water, and blue is for cold water. Lastly, your gas valve should be yellow. When they’re in the “On” position, the valves should run parallel with the pipes. If they’re perpendicular to the pipes, they’re in the “Off” position.
Turn the Water and Gas Off
First, you should turn both the hot and cold water off by turning each valve’s handle until it’s perpendicular to the pipes. After the water is off, turn off the gas valve. Typically, the handle for the gas valve is yellow, so it should be pretty easy to spot. Next, put your bucket underneath the hot water valve. Now, you’re ready to drain the water heater.
Twist the drain cap on the hot water valve to the left until you’ve fully removed it, at which point old water will start flowing out of the unit and into your bucket. After all the water has drained out of the hot water side, you can replace the cap and repeat the above steps on the cold water side.
Connect the Hoses
Photo: aquaArts studio / iStock / Getty Images Plus / Getty ImagesNow it’s time for the hoses. Connect one hose to the pump that came with the kit and then lower the pump into the bucket, being careful to keep the power cord out of the water. Next, connect the other end of the same hose to the drain valve for the cold water.
Then, connect the second drain hose to the hot water valve, and put the other end of the hose into the bucket (it should not connect to anything else). You should be able to tighten the hoses by hand.
Add Vinegar, Submerge Pump, and Circulate
With the pump now in the bucket, pour vinegar into the bucket until the pump is submerged. Open both drain valves. Then, turn on the pump to circulate the vinegar and water through the unit for 30 minutes.
After the pump runs for 30 minutes, turn it off and remove it from the vinegar. Hold it above the bucket and allow any excess vinegar to drain out of the pump. Then, set the pump aside and dispose of the vinegar in the bucket.
Once that’s done, you’re ready to repeat the process. Place the pump back into the bucket and pour enough vinegar into the bucket to submerge the pump. Run the pump for another 30 minutes. In total, you’ll circulate vinegar through the unit for an hour (in two 30-minute sessions).
Note that the water heater will attempt to start, but it will not be able to fire because the gas is off. If an error code appears, do not reset it; this usually happens during this process and is completely normal.
Pro tip: Move slowly to avoid spilling vinegar on a concrete floor, as the acetic acid inside the vinegar may etch the concrete surface and leave a mark that you can’t wash off.
Flush the Water Heater Lines
Photo: Vladyslav Varshavskiy / iStock / Getty Images Plus / Getty ImagesNow that the pump has circulated the vinegar for at least an hour and you’ve turned the pump off, close the cold water drain valve. Remove the hose from the cold water valve and put the valve cap back on. As you did before, lift the pump out of the vinegar, keep it over the bucket, and allow it to drain. Set the pump aside and empty and rinse out the bucket.
Next, you’ll be flushing the heater of any leftover vinegar. Put the end of the hose connected to the hot water drain into the bucket. Instead of vinegar, this time you’ll fill the bucket with water and place the pump back inside. Open the valve to the cold water supply line and start the pump to flush the heater with clean water. Let the water circulate in the heater for at least five minutes.
Flush Remaining Components
To finish flushing out your unit, put your bucket under the water heater and open the drain valve on the bottom. Once no more water is coming out of your unit, you can turn off the main cold water supply valve and shut off the drain valve. Then, you can remove the drain hose and replace the drain cap.
Now is also a good time to clean the water filter, and these typically unscrew to release. If you want to double up on this DIY, remove the filter and clean it under running water to flush out any scale and debris. Then you can replace the filter (make sure you screw it back on tightly).
Turn On Water and Gas and Clean Up
Photo: Andrii Atanov / iStock / Getty Images Plus / Getty ImagesThe hard part is over! Finally, you can turn the hot and cold main valves back on and turn the gas on. You’ll also need to turn the water heater off and back on again to clear the error code that appeared earlier. Aside from any remaining cleanup, you’re done.
DIY vs. Hiring a Pro
Learning how to descale a tankless water heater is a relatively simple DIY for most people. Many plumbers charge between $45 and $150 per hour just for labor, and you’ll likely end up paying around $200 for materials after that. Since you only have to pay for the materials if you do it yourself, you could save some serious money by DIYing this one.
However, if you’re unsure that you have the time or expertise to tackle this task on your own, put down the bucket and hose and call a pro. After all, all of the hot water you use in your home runs through your tankless water heater, so it’s important to ensure that the unit is properly cleaned and reassembled. If you’re not up to the job or just don’t have time, calling a professional water heater repair technician near you is always a smart way to go.
Questions to Ask the Water Heater Pro
If you decide to leave the descaling to a pro, a local water heater technician near you should be able to handle the task easily. You might also want to consider asking some questions about your water heater while it is in your home. Here's a rundown of all the questions to ask a water heater pro both before and after they show up for an appointment.
Are you licensed and insured?
Can you provide a full inspection of my water heater?
What other routine water heater maintenance services can you provide?
Can you provide an estimate of the life span left for my water heater?
Does your work come with a warranty?
What is the average water heater flush cost?
Is the current water heater I have the best option for my household?
Can you provide me with a quote for water heater replacement cost?
Frequently Asked Questions
Both vinegar and descaling solution work well for cleaning mineral deposits, calcium, and limescale from your tankless water heater. Vinegar is a more cost-effective and non-toxic method but may not be as powerful as descaling solutions. Descalers are highly effective, but they can be toxic and cost more than distilled vinegar. If you use a descaler, make sure to invest in high-quality safety equipment (gloves, a face mask, and eye protection) before beginning.
You should descale and flush your tankless hot water heater at least once a year. However, you may need to descale more often if you live in an area with hard water. Descaling will help keep your tankless water heater running as efficiently as possible and prevent scale buildup from causing other problems. Ultimately, regular descaling will help you save on future maintenance and repair costs.
If you don’t descale and flush your water heater, then calcium, limescale, and other minerals can build up inside the unit. Eventually, pipes, lines, and other components may become clogged and corrode. Your costs to run, maintain, and repair your water heater can increase if you don’t descale and flush the unit. Not descaling your water heater may make it run inefficiently and could cause you to have to replace it sooner than if it were regularly maintained.
It’s critical to know what your homeowner insurance does and does not cover. Each policy is different, but often homeowners insurance will cover damage from an appliance that suddenly fails, although it won’t cover the appliance replacement. Coverage might also be voided if the appliance failure is due to a lack of maintenance on your end. Always read the fine print of your homeowners insurance policy to understand the rules, loopholes, and legalities of your coverage.
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