Rheem Tankless Water Heater Troubleshooting Manual

Rheem Tankless Water Heater Troubleshooting Manual [Complete Guide]

This guide on Rheem Tankless Water Heater Troubleshooting Manual will walk you through common problems, including: 

  • No Hot Water
  • Water Not Hot Enough
  • Water Too Hot
  • Getting Hot Water Inconsistently
  • Unusual Noises

Rheem Tankless Water Heater Troubleshooting Manual [Common Problems & Solutions]

Let’s troubleshoot the common problems and discover the solutions.  

1. No Hot Water

No hot water out of your tankless water heater will be a result of: 

  1. The unit isn’t on
  2. The water shut-off valve is closed or not completely opened
  3. Closed hot water faucet
  4. Frozen water piping
  5. Electric power to the unit is Off.
  6. Set the temperature too low
  7. Mixing valve malfunctions
  8. Error code displayed on the remote control
  9. Not enough water demand
  10. Dirty or clogged water filter
  11. Dirty fixture aerator
  12. Scale buildup in the heat exchanger
  13. Hot and cold water lines get reversed

How To Fix: 

1. Press the power On/Off button to turn on your tankless water heater. 

2. Check out the water shut-off valve and turn it on by rotating the valve counterclockwise. 

3. Turn on the  hot water faucet completely. Otherwise, the main burner will go to the Off position when the incoming water flow is inadequate. 

4. Thaw out the water heater piping. If needed, call a professional for further assistance. I recommend you wrap up the pipes with an insulating material to protect the piping from freezing. You can read this guide to learn what to do when the tankless unit gets frozen. 

5. Plug the power cord of the unit into a standard outlet or reconnect the power at the circuit breaker panel. 

6. Increase the water temperature. To do so, turn on the control by pressing the Power button. Then, shut off water and gas to the water heater by closing the shut-off valves. Next, continuously press the Up button until 120°F shows on the display. Hold down the Up button until ‘120’ starts to blink. Finally, press the Up button and hold it down for 5 seconds (while 120 is blinking) to set the temperature above 120°F. 

7. Inspect the mixing valve and replace it if needed. 

8. Read this article on Rheem Tankless Water Heater Error Codes. 

9. Maximize the hot water flow at the faucet. 

10. Clean the water filter. Regarding this, turn off power to the unit. Remove the water filter from the base of the cold water inlet line. Then, clean the filter under running water. For removing sediment, you can use a brush to remove the buildup. Once you clean it, reinstall it. To learn more, read this guide

11. Clean the fixture or faucet aerator. To know the steps, watch out this tutorial.

12. Call a certified service personnel to inspect the heat exchanger. 

13. Reverse the water hose connections. 

2. Water Not Hot Enough

You will get insufficient hot water from your tankless unit if: 

  • Set the temperature too low
  • The gas valve is partially opened
  • Low inlet gas pressure
  • Bleed-over in one of the hot water fixtures

How To Fix: 

To resolve this water heater problem, go along with the following troubleshooting steps: 

  • Increase the water temperature at the remote control. In this case, turn on the remote control. Hold down the Up button until the 120 shows on the display. Then, continuously press the Up button until the 120 is blinking. Now, press the Up button again to increase the water temperature. 
  • Open the gas valve fully by turning it counterclockwise.
  • Call your gas utility company to adjust the gas pressure or get a continuous gas supply. 
  • Contact a certified technician for further assistance. 

3. Water Too Hot

Your tankless water heater will warm the water excessively if you set the temperature too high. Besides, partially open the water shut-off valve and small amounts of water are responsible for the unit to produce too hot water. 

How To Fix: 

First, reduce the water temperature at the remote control. Then, check the water shut-off valve and ensure you open it fully. Additionally, increase hot water flow at the faucet to maximize water flow through the unit. 

4. Getting Hot Water Inconsistently

You will get inconsistent hot water from the water heater due to scale buildup, temperature fluctuations, and gas supply issues. 

How To Fix: 

If you live in hard water areas, install a water softener to avoid frequent scale buildup issues. Second, descale your tankless water heater periodically to maintain its optimum performance. 

I recommend you insulate the hot water lines to minimize temperature fluctuations. If required, adjust the temperature settings to get a consistent hot water supply.

Lastly, ensure you have stable gas pressure.

5. Unusual Noises

A tankless water heater can make a rattling or unusual noise if scale forms in the water heater, irregular water pressure, or the burner gets clogged. 

How To Fix: 

Descale your water heater periodically and install a water softener if the water contains minerals. Next, ensure the water pressure is within specifications. Lastly, inspect the burner and remove the blockage from it. 

How Do I Reset My Rheem Tankless Water Heater?

Resetting your tankless water heater will fix issues like if your Rheem heater displays error codes. Follow the below steps to reset your Rheem tankless water heater. 

  • Just remove the power cord from the actual power source like the electrical outlet.
  • Leave your water heater for 30 seconds in a state of disconnection from the power source.
  • Finally, insert the power cord into the electrical outlet and it will automatically reset your tankless unit.


Every appliance is prone to malfunction. And your Rheem tankless water heater is not an exception to this. 

We broke down every defect or problem you may go through with your water heater over time. So, we recommend you bookmark this troubleshooting guideline. It will surely come in handy whenever you encounter a problem with your Rheem Tankless Water Heater. 

If you have any questions related to water heaters, leave a comment below. We will respond to you right off the bat. 

Read Also :


  1. User Manual: https://s3.amazonaws.com/WebPartners/ProductDocuments/F43535D0-25F4-4D07-980F-E035A8600BC9.pdf
  2. Tankless Water Heater Frozen: https://villageplumbing.com/blog/tankless-water-heater-frozen-heres-what-to-do/
  3. Rheem Tankless Water Heater Maintenance: https://lildutchuncle.com/rheem-tankless-water-heater-maintenance

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  1. I want to flush two units together. I was able to flush one but not able to flush the second one. Can you help?

  2. I need a picture showing where the reset button is at on my rheem performance platinum tankless wh . Im trying to make sure it even powers on before installing it but the controller doesn’t even come on.

    1. Thanks, Taylan Lowe for leaving a comment.

      To get access to the reset button on Rheem Performance Platinum Tankless Water Heater, you should remove the upper thermostat cover. Once you remove the upper cover, you can see the red reset button.

      You ask for a picture, but what if I give you a video link? Check out this video to locate the reset button on your Rheem Performance Platinum Tankless Water Heater:

        1. Sorry Met…

          Rheem tankless water heater has no reset button. To reset the unit what you need to do is- just unplug the unit from the power source and leave the water heater for 30 seconds. Then, restore the power to the unit which will automatically reset the unit. Hope, it will help you.

          And thank you for pointing out this.

  3. 10 year old Rheem tankless WH (RTG-74PVN) that won’t stay on. When I turn on the hot water, I can hear it light for 5 or 10 seconds but it then turns off. No hot water… I had a new Rheem unit installed today and it is doing the same thing. HELP. Water pressure seems to be good… Gas is on and flowing.

    1. The problem seems a bit complex. Do you install it professionally? I mean you should hire a professional to install the unit for you. Sometimes, reversed connections can cause this issue.

      The best suggestion I can offer is to call a certified plumber to have the unit checked professionally.

      Best of luck!

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