How To Flush a Tankless Water Heater? (13 Step Guide)

Last Updated On March 6, 2023
how to flush tankless water heater

If you made the upgrade to a tankless water heater, you get to enjoy the endless hot water, compact size, longevity, and high efficiency. 

Tankless water heaters come with a lot of benefits compared to storage tank water heaters, but they still require regular maintenance. 

Whether you have a tank-style electric water heater or the popular gas Rheem tankless water heater, you need to flush the tankless water heater regularly to prevent sediment buildup. 

In this PlumbingNav guide, we will cover: 

  • What you need to know about flushing a tankless water heater
  • Supplies you’ll need to flush a tankless water heater
  • How to flush a tankless water heater

What's In This Guide?

      What You Need To Know About Flushing A Tankless Water Heater

      Why You Need to Flush Your Water Heater

      Tankless units last up to 20 years on average, but sediment buildup can damage the different components of the water heater, especially the thermostat and heating element in the heat exchanger. 

      Hard water creates more calcium deposits than soft water, accelerating the damage to the water heater. The best way to remove limestone deposits in the device is to flush the water heater. 

      Flushing the water heater also ensures clean, potable water for your family to drink. The city uses a water filter before sending water out to the public, but your family can still end up drinking the deposits in the water, leading to health problems. The problem becomes a larger concern if the unit also shows signs of corrosion, getting rust into the water

      When to Perform Tankless Water Heater Maintenance 

      On average, experts recommend flushing a tankless water heater once a year, but it can benefit you to flush it more often if you have hard water

      If you know you have hard water, consider investing in a water softener that will eliminate minerals from your water before it enters your water heater. 

      Some signs it’s time to flush the water heater include: 

      • Discolored water 
      • Water with a rotten-egg smell 
      • Higher utility bills
      • High water temperatures

      Cost to Flush a Tankless Water Heater

      You can request professional plumbing services for tankless water heater maintenance that will cost upwards of $300 for each visit. 

      However, most people opt to flush their water heater themselves with the help of a tankless water heater flush kit that only costs one initial payment to flush the unit throughout its lifespan. 

      Supplies You’ll Need To Flush A Tankless Hot Water Heater

      Start by purchasing a tankless water heater flush kit. 

      Most kits come with a 3/16 hp (horsepower) recirculating pump, bucket, and hoses. Some kits will also come with a patented cleanser, but many people use vinegar as an alternative and see great results. 

      Outside of the kit, you may need basic household tools, such as a screwdriver. You may also need specialized plumber tape. 

      Wear clothing that you don’t mind getting wet and protect your electronics, especially your cell phone (you may need it to look up this article as a reference). . 

      did you know how to flush tankless water heater

      How To Flush Tankless Water Heater (13 Steps)

      Step 1: Turn Off Electricity/Gas

      Before performing maintenance on your tankless heater, you should always turn off the gas supply and turn off the electricity at the circuit breaker as a safety precaution. 

      If you leave the water heater on, you risk burning yourself or electrical shock. 

      When you turn the power off, give the water heater time to cool down. 

      Step 2: Close Cold Water Line Shut Off Valve

      Close the cold water supply valve at the top of the heater to ensure water doesn’t enter the unit until you are ready. 

      Step 3: Open Pressure Relief Valve to Release Excess Pressure

      Open up the pressure relief valve for a couple of seconds to allow excess pressure to escape the water heater. It will allow hot water to escape, too, so be careful not to burn yourself. 

      Step 4: Connect Hoses

      Connect one hose to the cold water inlet and the other end to the pump. Connect the second hose to the hot water outlet and place the other end in the bucket. 

      The idea is to create a constant flow of water between the pump in the bucket and the water heater. 

      Step 5: Place Submersible Pump in Bucket

      Put the pump into the 5-gallon bucket. It’s important that you use a submersible pump that can come into contact with water without getting damaged or creating a safety hazard. 

      Step 6: Fill Bucket With Cleanser

      You will now fill the bucket with 4 gallons of vinegar or your cleanser of choice. 

      If not using vinegar, always read the instructions carefully. You may need to mix a powder with water to create the liquid cleaning solution. 

      Step 7: Open Cold and Hot Water Valves

      Now that you have the hoses connected, you can open up the cold water valve again. You will also ensure that you have the hot water valve open. 

      Step 8: Run Pump

      Turn the circulation pump on for one hour (unless otherwise stated by the manufacturer). The pump will send the cleanser through the water heater, attacking the sediment buildup inside until it breaks down and flushes out of the unit. 

      Step 9: Restore Hoses

      After the pump runs for an hour, you can remove the hoses from the flush kit and restore the water heater’s original hoses. 

      Step 10: Clean Filter

      Many tankless water heaters come with a filter near the cold water supply to catch as much sediment as possible before it enters the water heater. You will need to remove the filter and clean it out under a faucet before putting it back. 

      Step 11: Tighten Connections

      Eliminate leaks by tightening the valves on your water heater using a screwdriver. 

      Some of the valves to tighten include: 

      • Purge port valve (purge valve)
      • Isolation valve
      • Drain valve
      • Shutoff valve
      • Service valve
      • Flush valves

      You will also tighten the hoses, especially the drain hose. 

      Step 12: Restore Power

      Turn on the electricity and the gas supply to the water heater. This will allow the water heater to heat your home’s water again. 

      Step 13: Verify Hot Water 

      Verify that you have hot water after putting things back to normal. Tankless water heaters provide hot water on demand, so you don’t need to wait to learn if the device is working properly.

      FAQs For How To Flush A Tankless Water Heater

      Do tankless water heaters need to be flushed?

      Yes! Both an electric tankless water heater and a gas tankless water heater need annual flushing as part of their regular water heater maintenance. 

      What do you use to flush a tankless water heater?

      Vinegar or descaling solution and a sump pump. 

      How much does it cost to flush a tankless water heater?

      A kit may cost $100 – $250 but last the duration of the water heater. 

      How much vinegar does it take to flush a tankless water heater?

      You will use 4 gallons of vinegar in a 5 gallon bucket.

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      We write about “all things plumbing,” helping you navigate common questions, repairs, and the best plumbing products on the market.

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