Rinnai tankless water heater maintenance: Clean and Descale

Learn how to perform Annual maintenance on Rinnai tankless water heater by cleaning and descaling the unit to improve the efficiency and lifespan.


This ultimate Rinnai tankless water heater maintenance manual will show you how to perform flushing and cleaning of the unit annually or periodically to keep it working like a brand-new heater and avoid costly repairs. This manual will tell you when to schedule the maintenance and do it yourself without spending lots of time and saving some money.

In this article our Chief Plumber Joseph will guide you with easy step-by-step instructions to perform a smooth and stress-free maintenance to your heater. Before getting errors and malfunctions on you heater, perform your heater maintenance today to enjoy uninterrupted hot water service.

Why to perform maintenance in Rinnai Tankless Water Heaters?

Scales and mineral buildup

Tankless water heaters have the heat exchanger, it consists of small metal pipes where cool water is passed through them and heated at high temperatures of up to 199,000 BTU to get instant hot water in our faucets.

As we heat water daily for our needs and water flows continuously through the heat exchanger when there is a demand of hot water, eventually scales are formed on the surfaces of heat exchanger pipes. Scales are the mineral deposits of magnesium and calcium found in hard water. These scales reduce the efficiency of water heating which eventually cause damage to the heater.

There are Various factors which influence the formation of scales, such as water temperature, flow rate, and the concentration of minerals in the water. High water temperatures and low flow rates will accelerate the formation of scales. So, removing the scales with a process called descaling must be performed for at least one year to keep your heater in good condition.

Dust, Insects, and debris

Air contains dust and debris, which can enter the heater unit through air intake pipes and get stuck at filters, which further gets blocked and doesn’t allow fresh air to get in, which can cause problems, and the heater pops out error codes. To avoid that, we need to clean the filters and pipes regularly.

Rinnai tankless water heater maintenance: Inspect, Clean, and Flush

In this guide, we are taking the example of the Rinnai RUR199iN but generally, all the other Rinnai tankless models work nearly the same. So, you can follow the below steps to maintain them easily.

rinnai tankless water heater outer parts classification rur 199

Tools required:

  • Screwdriver
  • Channel lock Pliers
  • A Tooth Brush to clean
  • Pair of washing machine hoses
  • 3 Gallons of White vinegar
  • 5 gallon plastic bucket
  • 1 Small Submersible pump between 1/5 to 1/6 HP.

You will need a Screwdriver, a channel lock plier, and two clothes washer(washing machine) hoses. These can be easily obtained from amazon or any hardware shops. For flushing and descaling, you will need 3 gallons of food grade white vinegar, don’t use any chemical solvents which can cause heath issues as we use this water for cooking and bathing. After your first year, it is recommended to purchase a small sump pump which costs between $50-$60. It is important to ensure that the pump has a hose tap on the top to connect directly to one of the washing machine hoses. Make sure to choose a low-capacity pump like a 1/6 or 1/5th horsepower pump, so the vinegar can descale the heater slowly rather than pushing through too quickly and not effectively cleaning it.

The below table consists of components and tools used in maintenance process, we also included the best buy links.

1Descaling Flush Kit with pump
2Channel Lock Pliers
3Philips Screw Driver
4White Vinegar
5High Effective descaling solution
6Cleaning Brush
7Washing machine hoses 6Ft
8Rinnai cold water inlet filter

1. Inspect the heater, air intake and exhaust pipe

Inspect for error codes:

First, inspect the heater unit for any error codes in history. To check error history press power button once and press the down arrow key. If you found any, look for the manuals or error codes chart. If the error is complex to solve and within the heat exchanger, you need to call a professional.

investigate the rinnai tankless water heater error codes history


It is recommended that complex tasks linked with heat exchangers or gas pipes must be fixed only by licensed professionals. If you see no errors follow the next steps.

Inspect for water leaks:

Look for any water leaks. If you found any, look from where the water is leaking, so you can analyze whether you can do it or call a professional. If no water is leaking, follow the next step.

Inspect the Inlet and exhaust pipes:

Inspect the outer ends of the air intake and exhaust pipes for blocks. If they are blocked by something, try to clear them.

2. Remove the front panel

To remove the front panel, first, we need to remove the plastic side guards from the heater by pulling them sidewards from the unit. Be careful while removing them. If you pull them towards the front, hook tabs can break. Once both side guards are removed, you will see four screws near the hook tabs. Remove the screws of the front panel with the help of a screwdriver.

After removing the screws, pull the bottom of the front panel out towards you and lift it upwards so that the front panel is removed and you can see the inside parts of the unit.

3. Clean the Air intake filter and inspect the flame rod

rinnai tankless water heater air intake filter location

If you look inside the heater, at the top, there is a small metal box for air intake through which the air comes inside the heater and feeds to the turbo. There is an air intake filter made of stainless steel mesh on the metal box to prevent small debris and insects from entering the heater unit. So, pull the filter out and look for dust or debris, clean it with a toothbrush and put it back again in its place. If the mesh has any sticky particles, you can clean it under tap water, but remember not to put the filter back in wet condition; dry it completely and place it.

Inspect the flame or flame rod(for gas units):

investigating flame in rinnai tankless water heater

On the heat exchanger there is a sight glass through which we can see the flame inside when the heater is running. The flame should be in clean blue color even though the other parts glow in red. If the flame is in yellow or orange color that could be a problem. You can call a professional to solve it.

Now you can put the front panel back on it. Locate the latch on the top of the unit and move it into place so that the screw holes align. This will ensure that the bottom window will fit properly with the hole in the heater. Then, insert the securing screws and replace the side guards.

4. Flushing and Descaling Rinnai tankless water heater

The manufacturer recommends flushing the heater annually, but if your area has higher hard water, we should do it twice a year. If scales are built up inside the heat exchanger, causing any issues, the heater pops out error code related to water pressure on the font display. If you are unaware of flushing Rinnai tankless water heater or flushing the heater for the first time, don’t panic. Follow the below steps, which will help you to descale your heater easily.

Step1: Turn off the heater and isolate the heater

Press the power button, which is the bottom right button on the control dashboard. It turns off the heater.

turn off and isolate rinnai tankless water heater

Next, Isolate the heater from the cold water intake and hot water outlet. The heater can be isolated by turning off the isolation valves on the cold water inlet and hot water outlet pipes. If the valves are parallel to the pipe, it is in ON condition, So turn the two cold and hot water valves perpendicular to the pipes, which forms a T shape to turn OFF and isolate the heater from the water flow.

Step2: Connect clothes washer hoses and drain water

drain water from rinnai tankless water heater

Now connect clothes washer hoses to cold and hot service drain outlets and keep the other ends of hoses in the 5-gallon plastic bucket. Next, open the service drain valves to drain the water completely from the heat exchanger and internal pipes. Keep them aside for at least 5 minutes to completely drain off the water.

It is important to note that the water coming out from drain may be hot, so avoid touching them directly.

Step3: Clean the cold water inlet filter

rinnai tankless water heater cold water inlet filter

Just before the cold water inlet connection, there is an Inlet water filter in black color and made of plastic with steel mesh. With the help of the channel lock, slightly loosen it and take it out with your hand. Look for dust or debris, clean it, and put it back again. First, tighten it with your hand and then use a channel lock plier to tighten it like a 1/8th turn slightly. Don’t tighten it hard, as it is made of plastic it can break.

Step4: Flush the water heater to descale it

The final step is to flush and descale the heater. Place the sump pump inside a bucket, attach the cold side inlet to the top of the pump, and tighten it securely. Fill the bucket with three gallons of white vinegar.

flushing rinnai tankless water heater with vinegar and sump pump

The sump pump, connected to the cold water inlet hose, will pump White vinegar through the hose into the cold water inlet of the water heater unit. The White Vinegar will flow through the heat exchanger and internal pipes to descales the mineral sediments. The vinegar, along with dirt and scales, leaves through the hot side and is diverted back into the bucket through the clothes washer outlet hose.

We will run this circulation of white vinegar through the system for 45 minutes to thoroughly descale the heater.

Step5: Purge vinegar out from the heater

purging vinegar after flushing in rinnai tankless water heater

After flushing, we need to purge the vinegar out from the heater. To do so, close the service drain on the cold side and then connect the clothes washer hose from the hot side to drainage and open the cold water intake valve. The Fresh cold water will purge the remaining vinegar out into the drainage. Run this for 1 or 2 minutes so the heater is cleaned with no vinegar.

Step6: Finalizing and turning on the heater

Finally, turn off the service valves and remove the clothes washer hoses. Turn on both the cold water inlet and hot water outlet valves. Next, turn on the heater by pressing the power button on the heater’s front panel dashboard. Set the temperature to maximum and check the faucets for hot water.

With all these, service maintenance on the Rinnai tankless water heater is done and ready to use.

If you see no hot water coming right after flushing, reset the heater and check for hot water.

If you have any questions or concerns, don’t hesitate to leave a comment below! Our team will assist you and provide all the information you need. Stay updated for our next article.

Joseph Miller

Joseph Miller is a highly experienced water heater repair expert with a passion for keeping homes warm and comfortable. With over 50 years of industry expertise, Joseph has developed a deep understanding of water heater systems and the intricacies of their repair and maintenance.

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  1. Thank for very detailed explaination. It helped me a lot, and by the way can i use CLR Calcium Lime & Rust Remover instead of white vinegar for descaling.

  2. We are in the process of doing this now and there is no vinegar coming through the hot water line into the bucket. We have followed every step listed. Help!

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