rheem tankless water heater error codes

Rheem Tankless Water Heater Error Codes [The Complete Guide]

This is a complete guide on Rheem Tankless Water Heater Error Codes. In this guide, we will describe the common error codes this tankless water heater displays. Besides, we will also depict those reasons that trigger the error messages and provide the solutions as well. So, let’s get started right here.

Table of Contents

Rheem Tankless Water Heater Error Codes [A Complete List]

Rheem tankless water heater starts malfunctioning over time. When there is any problem with the unit, it will pop up an error code on the display. It helps us diagnose and determine the exact problem with the water heater. From this chapter, you can learn about the most common error codes the tankless water heater shows. We also break down how to clear those error codes from the display. So, keep reading. 

01. Error Code 03

Rheem Tankless Water Heater Code 03 indicates an issue with EZ Link. It occurs due to: 

  • Loose communication cables 
  • The 4 dip switch is in the off position. 

How To Fix: 

You can easily reset this fault code by checking the communication cables. Ensure those cables are secure & tight. Next, inspect the #4 dip switch setting and verify it’s in the On position. 

02. Error Code 05

An imperfect combustion alarm is what the error code 05 means. This error code will flash on the controller display because of: 

  • Dirty air inlet filter
  • Dirty combustion air fan
  • Filthy heat exchanger fins
  • Clogged air ventilation openings
  • Blocked vent system 

How To Fix: 

Do the following tasks to reset the error code 05: 

  • Clean the air inlet filter
  • Inspect the combustion air fan and use an air compressor to clean the dirt buildup.
  • Clean heat exchanger fins
  • Check the air ventilation openings and clean them if necessary
  • Clean the vent system

03. Error Code 10

Error code 10 indicates abnormal low-rate combustion. Your tankless unit will go through this issue due to one of the following reasons: 

  • Improper vent component connection
  • Blockage in the flue inlet or exhaust
  • Improper condensate drain installation
  • Clogged air intake 

How To Fix: 

Follow these troubleshooting steps to reset the error code 10: 

  • Ensure all the vent component connections are okay
  • Release the blockage from the flue inlet or exhaust
  • Verify your plumber installs the condensate drain properly
  • Clean the air intake 

If required, call a certified technician for further assistance to clear the error message 10. 

04. Error Code 11

No ignition at start-up is what the error code 11 resembles on the Rheem Tankless Water Heater. The unit will flash this fault code on the controller display if: 

  • Defective igniter coil
  • Faulty igniter
  • Insufficient or restricted gas flow
  • Improper gas pressure
  • Gas solenoid valves are at fault
  • Damaged igniter wire harness
  • Ventilation issues
  • Dirty flame rod sensor

How To Fix: 

To reset the error code 11, follow these troubleshooting steps: 

  • Check the igniter coil for visual damage and replace it with a new one. 
  • Replace the igniter
  • Ensure the gas supply to your home is On. Then, check the gas valve of the water heater and turn it counterclockwise to let the gas flow to the unit. 
  • Get a manometer and check the gas pressure. The gas pressure should be within the specification. 
  • Replace the gas solenoid valves
  • Replace the igniter wire harness
  • Clean the flame rod

Explore the details: Rheem Tankless Water Heater Code 11

05. Error Code 12

Error code 12 on tankless water heater means flame failure. The tankless unit will pop up this warning message due to the following reasons: 

  • Dirty flame sensor
  • Insufficient gas supply
  • Improper inlet gas pressure
  • Gas lines too small for the BTU load
  • A defective gas control valve
  • Clogged venting
  • Defective flame rods and heat exchanger

How To Fix: 

Addressing and fixing those issues we mentioned will help you eliminate the error code from the display of the unit. We recommend you read our in-depth guide on Rheem Tankless Water Heater Code 12. In that article, we described everything that causes your water heater to trigger the error message 12. Also, we broke down the troubleshooting steps to clear the message. 

06. Error Code 13

Poor combustion is what the error code 13 means. It appears on the controller display due to: 

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

How To Fix: 

To reset this error code, do these remedies: 

  • Clean the water inlet filter
  • Clean the exhaust vent
  • Use a tiny drill bit to clean the burner orifice
  • Clean the combustion sensor 
  • Fix the ignition problems

Explore the details: Rheem Tankless Water Heater Code 13

07. Error Code 14

Fault code 14 on tankless water heater means the Overheat Film Wrap sensor has activated. If this sensor senses that the heat exchanger of your water heater gets overheated, it will pop up this error message. Improper fuel type, rusty or defective heat exchanger, and faulty Molex connector are some caveats responsible for triggering this error code. 

How To Fix: 

Most tankless water heaters are operated by natural or LP gas. It will be best to check the manual and use the fuel type recommended by the manufacturer. Secondly, take your eyes on the heat exchanger to see whether it gets dirty or not. If yes, clean the heat exchanger. Finally, ensure the Molex connector is in good condition. To learn more about error code 14, read this in-depth guide.

08. Error Code 15

The flashing code 15 on the controller display indicates a very high-temperature issue. Your tankless water heater will heat the water at high temperatures if: 

  • The water inlet valve is not fully open 
  • The heat exchanger gets covered with scale buildup

How To Fix: 

Ensure the cold water inlet valve is fully open. Also, verify the cold water inlet pipe is free from dirt and debris buildup. 

Second, flush the tankless water heater if the heat exchanger gets clogged. I recommend you read this article on Rheem Tankless Water Heater Maintenance to learn how to flush the unit. 

09. Error Code 16

Outlet temperature too high or over temperature warning is what the error code 16 indicates. It happens if the heat exchanger gets clogged or the vent terminal gets restricted. 

How To Fix: 

Check the heat exchanger for buildup and flush the tankless unit if needed. Second, ensure there is sufficient ventilation around the unit and the vent terminal is free of blockage. 

10. Error Code 21

This error code on the Rheem Tankless Water Heater indicates a problem with the air intake filter or the filter switch. 

As a remedy, ensure the air filter door is properly seated or verify you installed the front panel correctly. 

11. Error Code 24

When the unit flashes error code 24, understand the operational switch is at fault. To resolve this issue, I recommend you disconnect the remote control and retry. Also, verify the tankless unit is electrically grounded. Last, reset the unit by turning it on and off. 

12. Error Code 29

In the troubleshooting manual, Rheem says that error code 29 stands for too low heat exchanger outlet temperature. A clogged air inlet filter, dirty heat exchanger fins, and bad heat exchanger thermistor are some culprits behind this issue. 

However, there is also another meaning of the error code 29. It indicates a neutralizer drainage failure. This neutralizer is specially designed to keep the drain condensate away from the water heater. If this drainage system gets clogged, your tankless water heater will flash the error code 29 to prevent the burner from being flooded. 

A clogged condensate drain line and incorrect condensate line piping are the common causes to block the drainage system. Nonetheless, freezing weather can also block up the neutralizer drainage system. 

How To Fix: 

Begin with cleaning the air inlet filter. Then, inspect the heat exchanger fins for a clog and release the buildup. 

Next, check the resistance of the heat exchanger thermistor. The resistance of connector R between #Black3 and #Yellow5 wires will be 4K to 10K ohms. If you don’t get this reading, you should replace the heat exchanger thermistor. Otherwise, you need to change the PCB. 

On the other hand, you should get a neutralizer kit and install it on your water heater if the neutralizer drainage fails. Installing the kit on the water heater will treat the condensate properly for safe disposal into the drain. Ensure the condensate flow is free of dirt, debris, and buildups. On top of this, you must ensure the drain will not allow backflow. 

During winter & freezing days, we recommend you insulate the drainpipe by using a heat tape. It will be better if you install the heat tape close to the exit to the main drain to get the best output. 

13. Error Code 31

Inlet thermistor open circuit is what the fault code 31 means. It pops up on the controller display if the sensor wiring comes loose or gets dirty. 

To reset this error code, verify the sensor wiring is correct and secure. Also, ensure the sensor wiring is free from dirt and debris. 

14. Error Code 32

The meaning of error code 32 is faulty heat exchanger temperature sensor. It appears on the display when the wiring of this sensor gets damaged or dirty. To erase this code, verify the temperature sensor wiring is tight, and there is no scale buildup on the sensor. 

15. Error Code 33

Fault code 33 means outlet thermistor open circuit. It occurs if the outgoing water temperature sensor wiring is at fault or dirty. You can easily erase this error code by ensuring the sensor wire is tight and free from scale buildup.  

16. Error Code 34

Ambient air thermistor open circuit is what the fault code 34 resembles. Dirty or loose ambient air temperature sensor wiring is the culprit that causes the unit to throw this error code. 

To fix this issue, ensure the wiring of the ambient air temperature sensor is secure & tight. Also, verify the fan blade is tight on the motor shaft.  

17. Error Code 35

Your tankless water heater will display the error code 35 when the thermistor connections get crossed. By connecting the thermistor connections to the appropriate terminals on the PCB, you can erase this fault code. 

18. Rheem Tankless Water Heater Code 65

Water volume control fault is what error code 65 indicates. A defective or loose wire connection between the water control and the connector B on the PCB is the main culprit that causes your heater to pop up with this error message. Besides, faulty water control assembly is another reason responsible for flashing the error code 65. 

How to Fix:

As a basic inspection, start with verifying that there is water flow through the unit. Next, access maintenance information to determine the flow rate.  

Afterward, measure the voltage of the wiring between the water control and the connector B. The voltage should be 8 to 16 VDC. If you don’t get this reading, you must replace the PCB. 

If you get the voltage reading, take another measurement at connector B between the White#2 and White#8 wires. If you don’t get the appropriate voltage reading (8 to 16 VDC), you should replace the water control assembly. 

19. Rheem Tankless Water Heater Code 76

Error code 76 on Rheem Tankless Water Heater is an indication of faulty communication with the remote control. Your water heater will flash this error message on the control panel due to: 

  • Loose remote control wiring or the remote control itself gets defective
  • A bad filter capacitor

How To Fix:

Firstly, determine whether there is a problem with the remote control wiring or the remote control itself. If you don’t know how to detect the source of the problem, you can read this guide. We also broke down what you should do if the capacitor gets faulty. 

20. Rheem Tankless Water Heater Error Codes P1

Your Rheem tankless water heater will trigger the P1 error codes if there is a lack of sufficient water flow to activate the unit. If the inlet screen at the cold water connection gets clogged with dirt & debris, the water will not flow through it. Besides, your water heater will throw the error code ‘P1’ if the water flow sensor goes bad. 

How To Fix: 

Hire a plumber and tell him to clean the inlet filter at the cold water connection to the unit. On the other hand, if you want to save money, check out this video to learn how to clean the inlet filter. 

After cleaning the inlet filter, run the hot water only in the tap to check. If the water doesn’t flow, we recommend you increase the flow rate. Otherwise, you should replace the water flow sensor. Watch the following tutorial to learn how to replace the water flow sensor. 


What does E5 mean on my Rheem tankless water heater?

E5 on a Rheem Tankless Water Heater means there is a high flow rate. It means the desired water volume is too high that exceeds your desired preset temperature. To fix this issue, you need to slow down the flow rate. To learn further, read this article: Rheem Tankless Water Heater E5 Code.

How do you clear the error code on a Rheem tankless water heater?

Resetting your tankless water heater will help you clear the error code from the control panel. To reset the water heater, turn off the hot tap water and the unit itself. Leave the unit for 2o minutes. Then, turn on the water heater again, which will reset the heater. If it doesn’t erase the error message, fix the issues that cause the heater to pop up the error code. Then, reset the Rheem tankless water heater again. 

What does E4 mean on a Rheem tankless water heater?

E4 on your Rheem tankless water heater indicates an issue with the flow meter sensor. If the flow meter sensor gets defective, the unit fails to send a signal to the computer that is responsible for starting the device. 

Why is my Rheem tankless water heater beeping?

Your Rheem Tankless Water Heater will beep and show an error code if there is a problem with the unit. It will alert you that your water heater requires service or that there are damaged or broken components you need to repair or replace. 


Rheem Tankless Water Heater displays a lot of error codes due to specific reasons. Those error codes don’t only help you understand the actual problem with the unit but also make it a breeze to fix them. 

From top to bottom of this guide, we broke down every error code our tankless water heater displays. So, follow the troubleshooting steps we mentioned to clear the error message. 

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  1. good stuff mate i have a rheem gas 871624pfj tankless it comes with code e 51 ,i turn unit off it clears error code and will work and stay working untill you stop using hot water then back to e51,cleaned filters ,still same any help pls.

    1. Hey Don,

      The unit will throw the error code e51 if the gas inlet solenoid valve is at fault. In this case, check the followings:

      1. Inspect the gas valve wiring harnesses for loose or damaged terminals
      2. Ensure the connections to the circuit board are secure.

      Cycle your water heater two times by turning off- then turn on- at 10 seconds intervals.

      After cycling the unit if you notice any remaining flame through the view window, I bet the gas control assembly is the culprit. In this case, you must replace the gas control assembly.

      If you observe no remaining flame, don’t hesitate to check the relay connection of flame rod connector. Also, inspect the flame rod electrodes and clean them. Checking the main burner and cleaning it will also worth it.

      If nothing works for you, I suspect the PCB is the culprit.

      Hope this input will be helpful for you.


  2. Receiving error code 61 -Faulty Blower Motor. Did not see that error code here. Any help you could provide or resource you can point me to would be greatly appreciated. Thanks.
    Rheem Model RTG 84DVLP

    1. Hey CJ,

      I have just updated this article as per your request. Check the number 11 where I break down the error code 61. And thank you for mentioning your issues. I am glad to help.

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