Rheem Tankless Water Heater Code 13 [How To Fix]

Dirty flame rods are the main culprit that causes your Rheem water heater to throw the error code 13. Therefore, a defective ODS thermocouple and improper manifold gas pressure are responsible for Rheem tankless water heater code 13. 

Below, we will break down each of the culprits. As a result, you can easily clear the error message 13 from the display of your Rheem water heater. So, let’s get started right here to explore the way of removing the error code 13. 

Relevant: Rheem Tankless Water Heater Error Codes

Table of Contents

What Does Code 13 Mean On Rheem Tankless Water Heater?

Rheem tankless water heater throws the error code 13 if the ODS (Oxygen Depletion Sensor) gets activated. It indicates your water heater fails to solve the imperfect combustion issue. In other words, the error code 13 on Rheem implies there is a problem in your water heater’s combustion system. Though it’s not a regular water heater issue, we recommend you check the following beforehand: 

  • Inspect whether there is proper combustion air or not. 
  • Don’t forget to check your previous maintenance history to see whether it’s the first incidence of failure with this error code or not. 

Rheem Tankless Water Heater Code 13: Why & How To Fix

Don’t know how you fix code 13 on a Rheem furnace? Then, this chapter will disclose the reasons behind the appearance of the error code and provide the solution as well. Without further ado, let’s dive in. 

01. Flame Rods Issue

Dirty flame rods are the main culprit that makes your water heater throw the error code 13. If you don’t clean your water heater regularly, the flame rods will get covered with carbon buildups. Consequently, they fail to sense the flame from the burner. And it causes improper combustion. 


Cleaning the flame rods will be an easy solution to fix code ’13’ problems. Just get 100 grit sandpaper and gently clean the carbon residue from the flame rods. Keep in mind; you must disassemble the burner assembly to clean the flame rods. If you have never done this task before, watch the below tutorial that will help you a lot:

02. ODS thermocouple gets defective

A defective ODS thermocouple is also a culprit responsible for improper combustion. If the ODS sensor fails to sense the burner flame, you will never get sufficient heat output. The Oxygen Depletion Sensor starts malfunctioning for the following reasons: 

  • The heat exchanger or venting gets clogged by dirt, debris, and deposits.
  • The fan motor gets blocked by dirt buildups. 
  • Also, inspect the air intake for blockage.

How To Fix:

Firstly, inspect the heat exchanger for deposits buildup. If you find any blockage, release it by cleaning the heat exchanger. Also, don’t forget to check the venting as well. Insects like spiders can make a home in the venting. So, clean the venting system. 

Secondly, clear the blockage inside the fan motor. And finally, clean the air intake system. Otherwise, it will not circulate fresh air for proper combustion. 

On the other hand, if the ODS thermocouple is okay, we bet your water heater is normal. Just turn it off and operate the heater again. 

03. Abnormal Burner Manifold Pressure

Correct manifold pressure is indispensable for proper combustion. If the manifold pressure is not normal, you will get improper or poor combustion that triggers the error code 13. 

However, the manifold pressure will vary depending on the fuel you use to operate your water heater. If you use natural gas for running the Rheem Water Heater, the maximum manifold pressure should be 3.5″ w.c, and the minimum gas pressure should be 1.8″ w.c. 

On the other hand, the max LP gas manifold pressure should be 10.0″ w.c, while the minimum pressure should be 4.9″ w.c. 

If you don’t get this manifold pressure after measuring with a manometer, you must adjust the manifold pressure. Below, we will let you know how to adjust the manifold pressure in the ‘How To Fix’ section.

How To Fix:

Adjusting manifold pressure is not rocket science. Just follow the below step-by-step instruction: 

  • Turn off the gas flow at the manual gas valve.
  • Use a 3/32 Allen-head wrench to loosen the outlet pressure tap plug. 
  • Now, grab a manometer and attach it to the pressure tap. Keep in mind; you should get a 5/16 I.D. hose for the pressure tap. 
  • Now, turn the gas supply on and operate your tankless water heater.
  • It’s time to adjust the manifold pressure. So, pull out the regulator caps and turn the adjustment screw clockwise to increase the pressure. The manifold pressure shouldn’t exceed 3.5 w.c if you run the water heater with natural gas. You can also decrease the pressure by turning the adjustment screw counter-clockwise. 
  • Once you adjust the manifold pressure, put the regulator caps back into their place. 
  • Then, turn the gas supply off at the manual gas valve and remove the manometer & hose. 
  • Finally, use a 3/32 Allen-head wrench to tighten up the Allen-head screw in the inlet pressure tap.

What If You Get The Error Code 13 but Fails To Locate The Problem?

We mentioned earlier that it’s an uncommon water heater issue. So, it’s normal sometimes you can’t figure out the exact reason behind this problem. 

In this case, we recommend you try out the following steps to check whether the sensor damper is missing or not. 

1. Make sure the wiring between ODS and PCB is tight. A loose wire connection may display zero voltage in maintenance mode. 

2. Recycle your tankless water heater to the main burner. 

3. Now, run your water heater for 3 minutes in the main burner mode. When running the unit in this mode, do you encounter the following problems:

  • The unit shuts off exactly at 2.5 minutes?
  • Don’t go to EC ’05’ to try to fix the issue?

4. If yes, do the following things:

  • Recycle power and head over to maintenance mode.
  • Head over to cell ØA
  • Ensure Ø voltage is present when the main burner is in the off position.
  • Head over to the main burner by pressing the On/Off button. 
  • Now, run a water faucet and operate the unit for 3 minutes and keep your eyes on the display cell ØA
  • The ODS and burner may be okay if you get between 8 mv and 30 mv. 

5. If you get any readings within 3 minutes and the reading drops below 8MV and heads over to Ø, we bet there is a problem with the ODS, missing sensor damper, or the burner. 

To solve this issue, you must replace the burner assembly. 

How To Reset The Code On A Rheem Tankless Water Heater?

Resetting the water heater can clear the error code 13 from the display. The below steps will help you reset the tankless water heater. 

  • Find the heater circuit by heading over to the electric panel. 
  • If the circuit has flipped off, flip it on. 
  • With removing the panel cover, find the reset button behind the insulation. 
  • Hold down the reset button inwards until it clicks in place. Then, release the reset button.
  • Put the panel cover back into its place. 
  • Turn on the gas valve. 
  • Finally, turn on your water heater and run it. We hope it will clear the error code 13 if you solved the problem by cleaning the flame rods. 


Why does my Rheem tankless water heater keep shutting off?

Your Rheem tankless water heater will keep shutting off due to a loose wire connection, a clogged gas valve, insufficient fuel, and a defective thermocouple. 

Why is my tankless water heater constantly running?

Your tankless water heater will constantly be running if there is a leak on the unit or its piping. Improper insulation and sediment buildup at the bottom of the unit may also be responsible for this issue. 

Why does my tankless water heater run out of hot water?

If you use multiple hot water appliances at the same time, we bet you will not get sufficient hot water from your tankless water heater. 


Error code 13 on Rheem Tankless Water Heater is an unusual heater issue. Dirty flame rods are the main reasons behind popping out the error message. So, we recommend you inspect the flame rod first and clean it. 

If the error code 13 still persists, head over to the other two troubleshooting steps. 

Finally, we recommend you replace the burner assembly if you can’t clear the error message after trying every step we mentioned.

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