How To Flush Tankless Water Heater (Gas & Electric)

by Curtis Grossi | Last Updated: March 19, 2024
Flush Tankless Water Heater

Flushing a tankless water heater is one of the maintenance chores that should be done regularly to optimize system performance. Failing to flush your tankless water unit can increase the fuel costs besides lowering the unit’s service life.

Make sure that your system is checked regularly by a professional to ensure all the complex and technical issues are addressed. On the other hand, it’s very easy to flush your hot water heater without involving an expert.

Knowing how to flush your hot water heater goes a long way in saving you money and that’s what we’ll be teaching you in this post.

How Often Should I Flush My Tankless Hot Water Heater?

You already know your tankless water heater must be flushed regularly. But do you know how often you should do it? It’s not just about how often, but why you should flush the tankless water. Many tankless water heater issues may push you to clean the unit.

The most common reason is to descale the unit and remove the accumulated hard water scales caused by cold water. If the water flowing in your tankless water unit is hard and the system is set to heat the cold water at high temperatures, you should flush the unit at least once every year.

We recommend you use white vinegar or solution to delime and descale the heat exchanger. Vinegar helps in breaking up the deposits Advanced tankless water heaters will update when they need descaling. If your cold water supply has no issues of hardness, you’ve to check the system for error codes regularly.

How To Know If My Tankless Water Heater Needs To Be Descaled?

Hard water is a big threat to every tankless water heater. Areas that receive cold water with higher levels of hardness require you to flush your heater often.

Not cleaning the unit regularly will leave them crippled, which could lower their lifespan and efficiency. There is no cause for an alarm if you live in an area that receives well water as very little damage will be exposed to the units.

Most tankless water units will send an alert when the flushing date is due. Watch out for error codes as well since some units will send indicators in the form of error codes.

How To Descale A Tankless Water Heater?

Descaling a hot water heater is a process that requires proper planning and a good amount of work. Even the thinnest scale build-up can prove a challenge to deal with. And considering the buildup of scale can increase your energy costs to a level you’ve never imagined, getting you the scale removed immediately after you discover it is crucial.

The reason tankless water heaters become inefficient after scale build-up is that it forces the heat exchanger to strain for it to heat the cold water to the required degree. It’s quite a serious mess that needs to be handled precautionary.

However, it’s not so complicated such that an ordinary homeowner cannot handle it. The process will prove pretty simple if you master what goes on inside the tank and what needs to be adjusted for the descaling process to be a success.

What Is Needed To Descale A Tankless Water Heater?

Steps To Descale Your Tankless Water Heater (Step By Step)

  1. The first step in cleaning a tankless water heater is to turn ON both the hot and cold water service ports followed by turning ON the submersible pump.
  2. Next, adjust the heating element to 150°F and allow the hot water to flow and circulate the vinegar for approximately two minutes.
  3. With vinegar having circulated all around the system, shut the water heater’s power off as well as the submersible pump.
  4. Close the isolation valves to ensure no more cold water or hot water flows in or out of the unit. Some units don’t have the isolation valve. Consider getting one and having it installed before you start the descaling process.
  5. Get your bucket ready for you to collect any available hot water while draining the heater. You’ll likely collect about one or more liters, depending on the amount of water available in the heater pipes.
  6. Drain everything available in the water heater. After connecting the unit’s hoses to the isolation valve remove the water in the bucket or get another bucket to mix the solution that will be pumped by the heater.
  7. Add water into your empty bucket using a garden hose and mix the descaling solution (vinegar). A half bucket of it will be enough.
  8. Get the two isolation valves A and B opened.
  9. Activate the sump pump. Allow the descaling solution to flow seamlessly inside your system. Letting it circulate for an hour will ensure everything gets descaled completely.
  10. Drain all the vinegar from the heater. Use fresh water to flush the remaining solution. Close valve B and open valve A to allow the remaining contents to flow into a bucket.
  11. Now, activate the inlet water valve to ensure the proper flow of fresh water into the heater. Keep the bucket on position to collect all the remaining descaling solution from the heat exchanger.

Why Should You Descale Your Tankless Water Heater Regularly

Descaling a tankless water heater may not seem important until you lose your equipment to scales and other avoidable problems. There are many reasons as to why you should descale your tankless water heater quite often and here are the five main reasons.

1. Ensure Optimal Performance

Tankless water heater manufacturers advise homeowners to flush their systems monthly to optimize performance. Descaling water heaters a month helps remove all the mineral scales, silt and sediment buildups.

When these elements build up inside your water heater, they strain its performance, reducing the speed at which water flows as well as its overall output. Flush your heater regularly to keep it clean and everything inside gushing efficiently.

2. Minimize Noise Level

Scale buildup is the main reason your water heater will start making those weird banging, popping and crackling sounds. The noises may stop on their own once in a while, but the problem will never stop until you get the unit descaled.

The weird sounds will disappear when the scale layer solidifies, making it impossible for the water to penetrate through. Soon after you notice funny noises coming from your water heater, the ultimate best way out will be to descale it.

3. Boost The Units Heating Speed

When foreign materials accumulate on your water heater’s bottom area, the heating process will slow down. In other words, when scales and electrodes build up on your water heater, its water heating efficiency will reduce.

That will affect the speed at which water is dispensed as well as the overall hot water output. A few minutes of water heater descaling can get the issue resolved and your water heater producing hot water at the desired hotness and production.

4. Lower The Units Operation Cost

When scales forms inside your water heater, your unit will face performance issues. It will have to struggle to output hot water at the desired pressure level. That will mean more energy being used and low water being outputted.

The more energy the unit uses, the higher your energy bills will go, and the more you will spend on repairs and maintenance. Why not save yourself the hassle by having your clogged and scaled water heater pipes and parts descaled regularly?

5. Increase The Unit’s Life

The more your system has to strain to output the desired hot water, the more damage the responsible parts suffer. Do not forget that every part of the water heater can only perform to specific levels and if it’s stressed to do more, its useful life will be threatened. Protect your unit from premature failure by getting it descaled every so often.

When Should You Hire A Technician?

Not every tankless water heater problem will call for professional intervention. However, complex issues beyond your amateurish knowledge should be left to qualified technicians. That’s if you don’t want to damage your water heater the more and end up paying more than you had budgeted.

The most common instance you must get your tankless water heater checked by a technician is when you cannot identify the problem. If your water heater is not heating water to the set temperature and does not respond after descaling, you must get a professional to check the unit.

As well, the water heater is making noises, and a cleaning does not solve the issue; it may signify a bigger problem in the motor or heater exchanger. Some heat exchanger and motor problems can be troubleshot following the right tips and guidelines, but some are way beyond the layman’s understanding. If the problem persists even after trying to troubleshoot it, the next wise step would be to hire a qualified technician.


If you’ve read this article to this far, it means two things – you have got a tankless water heater, or you’re planning on getting one. Whichever the case, preparing yourself for surprises and unexpected breakdowns is vital.

You don’t necessarily need to prepare yourself equipment-wise and skill-wise rather have the know-how on what should be done in case of such failures.

Our article intended to enlighten tankless water heater owners on how to descale their heaters and keep them functioning efficiently, and I am happy it has achieved that goal.

Curtis is the founder and owner of He is the lead guy concerning all the water-softening accessories in this site's guides and reviews. If he is not writing a reviews, guides or any other useful tips, you will find him testing them to find out their suitability. He is passionate about softening water. You will find him extremely helpful and always willing to educate the general populace all there is concerning water and its effects on their health and appliances.