How to flush a Rinnai tankless water heater in 10 steps

I'm writing this blog post to help people who have Rinnai tankless water heaters and are having issues with them.

There is nothing like a pleasant hot shower while the kids play outside. But when your bathroom isn't so nice, it can be frustrating not being able to enjoy an evening soak in the tub or take a warm bath.

Luckily, there are some simple fixes for those of us without plumbing degrees that will make you feel at home again.

10 Steps to Flush A Rinnai Tankless Water Heater

The 10 steps involved in flushing a Rinnai tankless water heater are as follows:

  1. Connect the hoses and verify connections are tight.
  2. Open the flushing valves by turning them at right angles (or perpendicular) to the current positions.
  3. Verify that rubber washers are in place and seal the connection between valves and tubing.
  4. Fill the bucket with clean water and turn on the sump pump.
  5. Allow the sump pump to run for 30 minutes if using a descaling solution or 1-2 hours if you are using vinegar.
  6. After flushing is complete, turn off the sump pump and discard the cleaning solution.
  7. Remove the caps on the flushing valves and dispose of them properly.
  8. Rinse the hoses with clean water and disconnect them.
  9. Close the shut-off valves and turn on the power to the unit.
  10. Test the unit by running water through it.

Things to keep in mind while flushing a Rinnai tankless water heater

Always turn off the power to your tankless water heater before cleaning. To properly flush it, turn off the water valves, address the purge port valve caps, and clean around the unit. The blue cold water valve should be addressed first, followed by the red hot water valve, and finally, the main valve that runs water into the house.

There are three valves - one for cold water (typically blue), one for hot water (red), and one for Purge (T-shaped handle). You must release the pressure inside the pipes slowly. Be careful not to move the sealing discs on the purge valves, or else they won't work correctly.

Take care releasing the pressure from the pipes - it may cause some hot water to come out. Make sure you turn off the hot water valve when flushing it. Connect the hosing lines to every valve on the water heater. At times, a sump pump may be needed to connect the hoses.

Don't forget to open purge port valves. Twist the cold/hot valves perpendicular to each other. You can use white vinegar for cleaning the water heater but never use chemical solutions.

The user manual has more information on flushing and draining procedures. The cleaning process should last no more than 45 minutes.

The purge port valves need to be closed, and the caps tightened firmly. Disconnect and put away all hoses from the valves before proceeding. Remember to tighten the caps firmly without over-tightening them.

You have to check the manufacturer's manual to see the correct way to restart the tankless water heater. You may only have to rotate and open the cold and hot water valves. The pipe should be cleared of any debris before starting this process.

The cleaning process should be started by turning on the hot water in a sink and letting it run until there is no more sputtering sound from the pipes. It will take a few minutes for the air bubbles to escape from the tankless water heater.

Why is it important to flush a Rinnai tankless water heater?

There are a few reasons why it is important to flush a Rinnai tankless water heater. First, it helps to remove debris and buildup from the system. This buildup can cause flooding, which can be a serious problem.

Additionally, annual inspections and maintenance are essential to prevent flooding. Finally, flushing a Rinnai tankless water heater can help to improve the overall performance of your system.

What are some of the benefits of flushing a Rinnai tankless water heater?

Flushing a tankless water heater is the most thorough way to maintain it. Regular flushing prevents sediment buildup, which can prevent regular heating operations and cause other problems. Additionally, flushing a tankless water heater with limescale is essential for its proper function and protection.

Water heaters are typically equipped with sensors and a diagnostic system that detects when limescale accumulates. If the water heater isn't flushed, it can damage the heat exchanger due to high temperatures. Limescale buildup is not covered by the warranty.

How often should a Rinnai tankless water heater be flushed?

Tankless water heaters should be flushed at least annually, but some manufacturers recommend flushing every six months, depending on the hardness of the water supply. The frequency of flushing may vary depending on the region and water quality.

What can happen if a Rinnai tankless water heater is not flushed properly or on a regular basis?

If a Rinnai tankless water heater is not flushed properly or on a regular basis, it can cause damage to the appliance. Damage to an appliance can lead to leaky appliances and wasted water. Flushing a Rinnai tankless water heater on a regular basis will prevent these issues from happening.

Are there any special considerations that need to be made when flushing a Rinnai tankless water heater?

Yes, there are a few things to keep in mind when flushing a Rinnai tankless water heater. First, it's important to use clean, fresh water when flushing the unit. This will help to remove any sediment or buildup that may be present in the unit.

Second, it's important to be sure that all of the water is drained from the unit before starting the flushing process. This will help to prevent any water from being left behind that could cause problems.

Finally, it's important to follow the manufacturer's instructions carefully when flushing the unit. This will help to ensure that the unit is flushed properly and that no damage is done to the unit.

How To Fix Rinnai Tankless Water Heater Beeping With No Error Code?

If a Rinnai tankless water heater doesn't display an error code, its alarm is sounding, and it isn't working, you can begin the repair by turning off the cold water but keeping the hot water tap open. But if power cycling of the unit doesn't solve the issue, proceed with the troubleshooting and repair by following these instructions:

Turn off the cold water but shut the hot water off. Remove the plug over the cold water valve. Clean the screen being covered up by the plug. Turn the cold water back on and wait for the unit to cycle through the startup sequence.

If this doesn't work, turn off the cold water again and then turn the hot water back on. Wait until the unit cycles through the startup sequence one more time. If this still doesn't work, replace the thermostat.

Watch How to flush a Rinnai tankless water heater

Frequently asked questions (FAQs)

1. What type of maintenance does a Rinnai tankless water heater require in general?

Rinnai tankless water heaters require exterior maintenance, such as checking for cracks or splits in pipe insulation.

It's a good idea to flush the water heater every 6 months and test the pressure relief valve if present. Maintenance typically takes about 20 minutes and can take longer if flushing is required.

2. Where can I find more information on how to properly maintain my Rinnai tankless water heater?

You can find more information on how to properly maintain your Rinnai tankless water heater in the Rinnai Owner's Manual or by contacting a qualified professional.

Q: Who should I contact if I have any questions about my Rinnai Tankless Water Heater or its maintenance requirements?

A: If you have any questions about your Rinnai Tankless Water Heater or its maintenance requirements, you should contact the manufacturer or a qualified installer.

Q: How much vinegar do you need to flush a tankless water heater?

A: Use 4 gallons (15.1 liters) of undiluted white vinegar to clean your tankless water heater. Never use chemical solutions of any kind.

Q: Is it normal for a tankless water heater to sometimes leak gas?
A: There are many different types of water heaters, but one of the most popular is a tankless or gas water heater. Leakage of gas is prevalent these days, and several people die every year due to the gas leak from the water heater.

Q: Do tankless water heaters need expansion tanks?

A: Most tankless water heaters (electric or gas) do not need a thermal expansion tank. The reason being is that a tankless water heater only produces hot water as requested. When the hot water supply is opened, the tankless unit starts to produce hot water.


A tankless hot water heater is a great way to save money on energy costs. They also provide a reliable source of hot water at any time without having to wait for a conventional water heater to warm up. However, they do require some maintenance and care. So, follow the above-mentioned tips to maintain it properly.


You may also like

How Often to Water Poinsettia

How Often To Water Poinsettia? Care Guide For Live Christmas Plant

The poinsettia is a popular holiday plant. Its bright red leaves and

​Read More
How to bath a dog without water waterev

How To Bath A Dog Without Water: 13 Steps (With Pictures)

A dog is a member of our family, and they deserve to

​Read More
How often do you water outdoor potted plants

How Often Do You Water Outdoor Potted Plants? – 12 Tips For Healthy Flowers

When determining if your plants need water, the finger-dip test remains the

​Read More
How often to water impatiens

How Often To Water Impatiens? New & Overwatered Impatiens Care & Tips

Impatiens (also known as busy Lizzy) are beautiful houseplants that are easy

​Read More
How often to water fruit trees

How Often To Water Fruit Trees? Young Fruit Trees Need Plenty Of Water

A fruit tree is a perennial plant that grows from a seed.

​Read More
How often to water an Orange Tree

How Often To Water An Orange Tree: Tips, Tricks, And Requirements

Orange trees are some of the oldest living things on earth. They

​Read More
{"email":"Email address invalid","url":"Website address invalid","required":"Required field missing"}

Check the articles below

December 9, 2023

The poinsettia is a popular holiday plant. Its

December 6, 2023

A dog is a member of our family,

December 1, 2023

When determining if your plants need water, the