How to flush a Rinnai tankless water heater

A Step-by-Step Guide to Keep Your Rinnai Running Like New!

  • There is a clear contrast between hot and cold water. Just imagine right in the middle of a shower the hot water replaces with cold water. How it feels like frustrating right? No one likes that. Another level of frustration is when washing hands. How it feels when you are waiting for your tap water to turn hot before you can finally wash your hands. Not good at all! A tankless water heater can save you all these troubles. 
  • A tankless water heater is exactly what you imagine it to be – a water heater without a tank. Instead of storing hot water in a tank and continuously heating it, a tankless water heater heats the water as it passes through the unit. This means you’ll never run out of hot water, and you won’t have to wait for the tank to fill up before you can start using hot water.

But that’s not all – a tankless water heater will occupy less space in your home because it has no visible or bogus tank attached. No more sacrificing closet space for a bulky tank! There are now electric tankless water heaters that will fit even into small houses.

And let’s not forget that a tankless water heater can be seriously energy-efficient. Since a tankless water heater heats up water only when it is to be used. It consumes less energy and delivers an eco-friendly heating service. Just like me, I am certain you do not want your energy bills going through the roof every quarter.

So, if you want endless hot water, more closet space, and lower energy bills, it’s time to switch to a tankless water heater. Trust me, your showers will thank you. While you make this legendary switch to a tankless water heater, bear it in mind that you must learn how to flush a tankless water heater, if at least you want to maintain its optimal performance. You want to attend to this need without the assistance of a repair company.

How to Flush a Rinnai Tankless Water Heater?

There are few tankless water heaters that can match and surpass the efficiency level of a Rinnai tankless water heater. Rinnai has been known to flow with ever-changing and fast-paced technologies seamlessly. They hold the record of designing and building the first and only non-condensing tankless water heater with a built-in recirculation pump. With this water heater, you get to enjoy the following features:

  • Consistent hot water supply: With a Rinnai tankless water heater, you’ll never have to choose between taking a piping hot shower, doing a load of laundry, or running the dishwasher. Hot water is always available.
  • Providing better value than a tank: With Rinnai, you enjoy consumer financing and rebates. They even last longer than their specified warranty and they are immensely energy-efficient.
  • Saves valuable space: A Rinnai is indeed small and mighty, the suitcase-sized wall units fit in tight, discreet spaces, freeing up more usable living areas in your home

While you enjoy all these mouth-watering benefits, you must remember the necessity of frequent maintenance. One of your routine maintenance is flushing the water heater. Doing this saves your tankless water heater from mildew and chronic dirt.

Why Flush Your Rinnai Tankless Water Heater?

For long-lasting optimum performance, you must flush your Rinnai tankless water heater. When you do this, you will certainly reap the benefits. If not flushed, the heat exchanger of your tankless water heater can develop mineral buildup over time, which lowers the unit’s efficiency and raises the possibility of damage. But all the hassles will be effectively avoided if you flush your heater as often as possible.

How Often Should You Flush Your Rinnai Tankless Water Heater?

You are often advised to flush your tankless water heater at least twice yearly. Still, you may have to do that flushing more than two times a year if you live in a hard water area- a hard water area produces water with an excess concentration of minerals. Conversely, you may not need to flush as much in a soft water area.  

What You’ll Need

No one goes to war without the proper artilleries. You need to be prepared for the flushing of your water heater before you venture into it. Items such as the flush kit, a hose, white vinegar, and a pump should be made available for this exercise. 

Step-by-Step Guide on How to Flush Your Rinnai Tankless Water Heater

Step 1: Cut out your power

First, let us ensure we are not exposed to the danger of electrocution before we flush our water heater. To effectively cut out power access to your unit, you only need to turn off the breaker that supplies the unit. It is important to do this to maintain some level of safety. Always remember that your safety comes first.

Step 2: Shut Off the Water Supply

If water finds its way into your unit while flushing is on, it may disturb the process. Hence, shut off the water supply to the unit by turning off the valve on the cold water line leading to the water heater. This will prevent water from entering the unit during the flushing process.

Step 3: Drain the Water Heater

Look under your Rinnai tankless water heater; you will find the drain valve there. Connect the valve to a hose and place a bucket or container on the other end to drain the waste from the hose.

Step 4: Install the Rinnai Tankless Water Heater Flush Kit

Every Rinnai tankless water heater has a flush kit that should be used when flushing the water heater. All that needs to be done at this stage is to attach the flush kit to the cold water inlet and outlet ports on the unit.

Step 5: Fill the Bucket with Vinegar

Fill a bucket with white vinegar and connect the pump to the bucket. Place the other end of the pump in the bucket containing the vinegar.

Step 6: Turn On the Pump

Now, you must allow the white vinegar to circulate through the tankless water heater. To ensure thorough circulation, the pump should remain on and leave the vinegar to travel through the crevices of the heater- allow this process to continue for up to 40 minutes, and you’ll notice the white vinegar turning brown. When this happens, it’s already breaking down the mineral build-up in the heater.

Step 7: Drain the Vinegar

Wait for at least 40 minutes, after you’ll drain the valve and allow the vinegar to escape completely. To drain effectively, you can open the drain valve allowing the vinegar to escape into your drain bucket. Vinegar can be quite corrosive and irritating to the skin. Hence, dispose appropriately Vinegar is also effective for cleaning your dishwasher filters.

Step 8: Flush with Water

After draining the vinegar, connect a hose to the cold water inlet and turn on the water supply. Allow the water to flow through the unit for at least 15 minutes to flush out any remaining mineral deposits and vinegar. You can also use a pump to circulate the water through the unit for more effective flushing.

Step 9: Turn Off the Water Supply and Drain the Unit

After flushing with water, turn off the water supply and disconnect the hoses. Open the drain valve and let the remaining water drain from the unit.

Step 10: Turn On the Water Supply and Power

Finally, you have successfully flushed your Rinnai tankless water heater. Turn the power back on and reconnect the water supply. Test for any leaks or parts not well tightened and proceed to enjoy your tankless water heater. It is as good as new!

Additional Rinnai Tankless Water Heater Flushing Tips

  • Remember that your Rinnai tankless water heater manual can easily be your first point of call when any part of it needs fixing. You can engage a professional’s services if the fault is problematic and too complex to fix.
  • If you must use vinegar to flush your tankless water heater, use white vinegar, it is safer than other types of vinegar.
  • While you flush your water heater, whether tank, less or not, look out for other faults that may be obscured, wear and tear and a blocked filter are some faults that can be uncovered in the process.

How Much Does it Cost to Flush a Rinnai Tankless Water Heater?

The standard price of the Rinnai tankless water heater varies. As per the market research, it varies between $100 to $250. However, this price may change due to factors such as inflation, necessary maintenance, and location.

Resetting a Rinnai Tankless Water Heater

If you encounter any issues with your tankless water heater after flushing it, you may need to reset the unit. To do this, turn off the power to the unit, wait for at least 30 seconds, and then turn it back on. This will reset the unit and allow it to operate normally.


A tankless water heater by Rinnai will serve your needs efficiently but may only maintain its efficiency level if adequately maintained. One of the ways to maintain your Rinnai tankless water heater, and any tankless water heater whatsoever, is to flush it regularly. When you flush regularly, you clear all residue of dirt and buildup that may impede its optimum performance.


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

The cost of flushing your tankless water heater may vary according to the technicalities of maintaining the heater, the location of its use, and other factors such as inflation. However, the standard cost you will most likely incur in this process will range from $100 to $200.

How much time does it take to flush Rinnai Tankless Water Heater?

It varies with the issue but a normal flushing time for a Rinnai tankless water heater takes 30 minutes to an hour. In this process the removal of mineral buildup and maintenance of optimal performance takes place.

How do I open up my tankless water heater?

If you are struggling to open the lid of your Rinnai tankless water heater, worry no more, help is here. The first step is to turn the device off for safety concerns. Then locate the front cover panel on the bottom of the unit. Unscrew the panel, and you should have access to the internal parts of your tankless water heater. While you do this, ensure to maintain all safety protocols to avoid hazards or damage to the machine.

Why is a tankless water heater better than water heaters with tanks?

A tankless water heater occupies less space because they do not carry a bogus tank like its counterparts. A tankless water heater heats water on the go, making it extremely energy-efficient. 

How do I fix my leaky water heater?

First, turn off the power supply or gas to the unit to fix a leaky water heater. Then, locate the source of the leak and tighten any loose connections or valves. If the leak persists, it may be necessary to replace the faulty part. If you’re unsure about any steps or feel uncomfortable working with the heater, it’s best to contact a professional for assistance.

How do I clean a tankless water heater by Rinnai?

Cleaning your Rinnai tankless water heater is an important maintenance task that can help to ensure its optimal performance and longevity. To clean the unit, turn off the power supply or gas to the heater. Then, gently use a soft-bristled brush or compressed air to remove dust or debris from the unit’s exterior. Next, flush the system with a descaling solution or white vinegar to remove any mineral buildup inside the unit. Follow the manufacturer’s instructions and safety precautions when cleaning the unit. If you’re unsure about any steps, it’s best to contact a professional for assistance.