Rheem Tankless Water Heater Code 13

Rheem Tankless Water Heater Code 13 [5 Reasons & Solutions]

Error code 13 on Rheem Tankless Water Heater means poor or bad combustion. The unit will throw this fault code due to: 

  • Dirty water inlet filter
  • The exhaust vent gets clogged
  • Clogged burner orifice
  • Dirty combustion sensor
  • Ignition issues

You can easily reset the error code 13 by addressing and troubleshooting those issues. And this guide will walk you through each troubleshooting step to resolve the combustion issue. 

Let’s scroll down. 


Rheem Tankless Water Heater Code 13 [5 Reasons & Solutions]

Here are the culprits responsible for Rheem Error Code 13”

1. Dirty Water Inlet Filter

Dirty water inlet filter screen

The water inlet filter is the first component you need to check if the unit flashes the error code 13. 

If the water inlet valve gets clogged by lint or debris buildup, no water can flow through the unit. Without sufficient water supply, the unit fails to start the combustion process. 

How To Fix: 

The water inlet valve or filter is on the front of the unit. 

Water Inlet Filter On Rheem Tankless Heater

To remove it, shut off the electric supply to the unit by tapping the power button on the controller. Then, unplug the power cord from the electric outlet. 

Second, close the cold water inlet valve and the hot water valve. Now, it’s time to unscrew the cold water inlet filter. 

Use your hand to remove the water inlet valve because it’s hand tightened. Don’t forget to put a plastic bucket under it to catch water drippings. 

Once you remove the water inlet filter, bring it under the sink and clean it with running water. 

Cleaning the water inlet filter or screen with running water

After cleaning the water inlet valve screen, reinstall it and tighten it up. 

Finally, turn on the cold water supply and the hot water supply. Next, restore the power to the unit.  

2. Venting Issues

Proper combustion of the unit requires an adequate air supply. If the venting system gets clogged, it can restrict the air intake and cause a combustion failure. 

How To Fix: 

Inspect the venting system and ensure nothing is blocking the vent. Remove any obstructions in the combustion air intake and exhaust vent. 

3. Dirty Burner or Burner Orifice

Clogged burner or burner orifice

A dirty burner or burner orifice is the caveat responsible for Rheem error code 13. 

Due to a clogged burner orifice, no gas can flow through the burner chamber to begin the combustion process. 

How To Fix: 

Cleaning the burner or burner orifice is the simple fix to this issue. But the heck is- it requires a lot of expertise and technical knowledge to clean the burner. 

However, if you are technically inclined, remove the burner. Inspect all the burner orifices to see whether they get clogged with white crud. 

Use a very small drill bit by hand to clean the gunk up from the orifice. You can check out this tutorial below as a helping hand: 

4. Combustion Sensor Gets Dirty

Debris or dirt from the burner may fall on the combustion sensor, which can make the sensor ineffective. As a result, the sensor fails to send a signal to the control board and flashes the error code 13. 

How To Fix: 

Unfortunately, it takes a lot of time and technical details to remove the burner and clean the combustion sensor. So, I highly recommend you contact a certified service guy to let him handle this issue. 

5. Ignition Issues

Ignition issues refer to gas supply problems, defective gas valves, or other components involved in the ignition process. If your tankless unit goes through these issues, it can cause combustion failure. 

How To Fix: 

Ensure your unit receives the right amount of gas supply. Don’t forget to check the ignition components, like the flame rod, igniter, and igniter plug. 

I recommend you check this article on Rheem Tankless Water Heater Code 11 to resolve ignition problems. 


What is error code 13 on a heater? 

Rheem Tankless Water Heater Error Code 13 means combustion failure. It indicates that your tankless unit fails to ignite or sustain the flame to heat the water. In short, error code 13 appears on the controller display, indicating that the unit has a problem with the ignition process. 

How can I troubleshoot an error code 13 on my Rheem tankless water heater?

Go along with the following steps to troubleshoot the error code 13: 

  • Check the gas supply and ensure you open the gas valve fully
  • Ensure the gas pressure is within specifications
  • Inspect the venting system and ensure there is no blockage
  • Inspect the ignition components like the igniter, flame rod, and ignition electrodes for damage

 How do I reset my Rheem Tankless Water Heater? 

Resetting the Rheem Tankless Water Heater is simple. Turn off both the electric supply and gas supply to the unit and leave the water heater for 30 seconds. Then, restore the power and turn on the gas supply. Next, turn on the water heater, which should reset the unit. To learn more about it, read this article: How To Reset Rheem Tankless Water Heater.

Can I reset my Rheem tankless water heater to clear Code 13?

You can reset your tankless water heater to clear the error code 13. However, if you don’t resolve the underlying issues causing the error code 13, this code will reappear. 


Combustion failure is what the error code 13 resembles. It occurs due to a clogged water inlet filter, venting problem, and dirty burner.

Follow each troubleshooting step I mentioned to resolve this issue. If the efforts fail to resolve the error code, contact Rheem Customer Service or a certified technician for professional assistance. 

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