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

Flushing your Rinnai tankless water heater is something you should do every year to prevent the buildup of minerals and deposits that build up in your water heater. This builds up from hard water and can cause problems in the future by blocking water in and out. Fortunately, installing a Rinnai water heater is a simple process: in most cases, a few tools and half an hour are enough. Here’s a step-by-step guide on how to turn on your Rinnai water heater yourself and save money while learning a new skill.

How to Flush your Rinnai Tankless Water Heater

Rinnai’s tankless hot water installation process begins with gathering the necessary tools to do the job properly. These may include, but are not limited to:

  • Small pipe wrench
  • Open jaw pliers
  • Three (3) 5 gallon buckets (one with a lid)
  • Two (2) washer hoses
  • Submersible pump capable of 4 gallons per minute
  • Four (4) gallons of white vinegar

Step #1

To start the process, the first step is to turn off the heater without the tank. This is important, because the water heater will start to absorb water if it turns on. If the system opens when this happens, the result will be chaos.

Step #2

The next step is to close the hot and cold isolation valves and connect the two hoses to the isolation ports. This allows the alcohol solution to pass through the valves and pipes.

Step #3

Then, the cold side of the remote valve is connected to the submersible pump. This will introduce the alcohol solution into the process and continue until the break is complete.

Step #4

Then, using the other hose, the hot part is connected to the stop, which will go into the bucket. The amount of solution that comes out of the process can exceed the amount of the pump, because it will remove the minerals and deposits left by the hard water. This is why the capacity of the bucket (5 gallons) is greater than the solution (4 gallons).

Step #5

Then, the wine is poured into the bucket and the submersible pump is turned on. This will cause the solution to spread throughout the system. Most manufacturers recommend soaking the process for at least 45 minutes, but longer is better, especially in areas with hard water.

Step #6

How to Flush your Rinnai Tankless Water HeaterIf a professional is hired to clear the system, they usually wait by the scarf to do other maintenance work. Rinnai tankless water heaters have components such as burners, burners (for gas) and heat exchanger fins. This is important, as these things accumulate dust and dirt because they are often found in the garage.

Step #7

After cleaning, the liquid solution is discarded. This is the purpose of the bucket cover. Once the extracted solution is in the bucket, it must be closed and sealed using a lid. In fact, some municipalities control the waste from appliances such as hot water heaters and water heaters, so it will be necessary to -conveying water out. Experts recommend that they review the local requirements for guidance.

Now any residual vinegar can be flushed out of the system. This time four liters of fresh water is put into the bucket with the pump and the fresh water is pumped through the system to the third waste bucket. The quantity introduced must be very close to the quantity discharged as the system must be free of deposits and mineral accumulations.

Step #8

The next step is to turn off the circulation pump and close the service door on the cold water inlet. Then the washer hose can also be disconnected from the service port. This will restore cold water circulation to the heater.

Step #9

The last step is to close the service door, remove the hose from the washer and reopen the isolation valve. The cold water inlet valve is then opened to allow fresh water to flush the system a third time, but this time the water does not need to be picked up.

Rinnai RU199iN

Rinnai RUCS65IP

Rinnai V65iP

Rinnai RU199iP Rinnai RUCS65IP Rinnai V65iP

Rinnai Water Heater Flushing FAQs

How often do I need to drain the hot water without a Rinnai tank?

The nature of tankless water heaters requires them to be drained from time to time. This is due to the minerals and deposits left by the hard water that provides the heat. It is estimated that about 80% of consumers in the United States use hard water for everything from drinking water to bathing. As such, for those who have a tankless water heating system, it is recommended that the entire system be flushed at least once a year. Some manufacturers recommend pumping the system every six months, depending on the water strength in the area.

Can I drain my tankless Rinnai hot water myself?

In most cases, absolutely. Flushing the system is simple and straightforward, but equipment and plumbing parts will be involved. For DIYers who have difficulty or are uncomfortable with plumbing tools and techniques, hiring a professional is a good idea. Refining the system requires only a few parts and tools, but the job will involve a few steps that must be taken to do it or the result will not be good.

What is the best way to flush a Rinnai tankless water heater?

This may depend on the skill of the person using the washing machine and following the instructions. For example, a handyman will be familiar with tools such as wrenches, screwdrivers, and tools. Rinnai tankless water heaters will require only a few tools and a few common items. For those new to DIY, another option might be to use a tankless water heater. These tools include the parts mentioned correctly and are universal. However, it is recommended that you follow the instructions that come with hot water without a tank, as some manufacturers require different measures to prevent damage to the unit.


Flushing out a Rinnai tankless water heater is designed to be relatively easy.  No special tools or training is typically required, so most homeowners can perform the task successfully.

The main things to keep in mind are to have the correct materials available, follow the manufacturer’s instructions carefully, and above all, be safe.