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Rheem Tankless Water Heater Error Codes

Rheem Tankless Water Heater Error Codes

Do you find a flashing code on your Rheem tankless water heater? Are you wondering what it indicates? Look below at some error codes and their meaning in this article.

Rheem tankless heaters are known for their top-notch quality. Once you have bought these heaters, you can expect them to function well for a longer period.

However, like other appliances, Rheem tankless heaters can run into trouble too.

The great thing about Rheem tankless water heaters is that they automatically flash a code on the display unit whenever a problem has been diagnosed. The code indicates an error that needs to be resolved.

To troubleshoot the appliance, you must know about these error codes.


Rheem tankless water heater errors are a way to indicate some problems with your Rheem tankless water heater. The error number is useful in identifying which part of the water heater has a problem.

Instead of operating the wrong part of your water heater when facing a fault, you can identify the error code, refer to that specific part, and correct it conveniently.

There are 18 Rheem error codes. You can refer to the displayed error code to rectify the specific problem with your tankless water heater.

This article will shed light on 18 Rheem tankless water heater error codes and how to troubleshoot them properly.

18 Rheem Tankless Water Heater Error Codes

Rheem whole-home tankless water heaters are great for homes with busy families. These heaters are also ideal for a single faucet or shower.

You can enjoy the comfort and convenience of on-demand hot water using Rheem tankless heaters. These tankless heaters come in a variety of models.

Whether you aim to provide hot water to your whole home or a single location, Rheem has a full range of options for each purpose. You can find the tankless water heater that best suits your needs.

The error codes on your Rheem water heater may trouble you for some time, but you will be happy to learn how easy it is to troubleshoot them and get your tankless water heater back to working.

The following are the error codes that your Rheem tankless water heater may display and how to correct them:

1. Error Code 00

Error Code 00

The error code “00” means that your Rheem Tankless Water Heater has been running continuously for over an hour.


When you see an error code 00, you must shut off all the hot water taps. In addition, if a circulation pump is installed at your place, you also need to turn it off.

2. Error Code P1

Error Code P1

Error code “P1” indicates that the water flow is too low.


Check the hot water tap flow and clean the aerators. You can also clean the water inlet filter, increase the flow rate, and set the temperature higher.

3. Error Code 1L

Error Code 1L

Whenever a limescale accumulates in your Rheem tankless heater, an error code “1L” flashes on the front panel.


To clear this error, maintenance is required. It would be best if first, you flushed your tankless water heater to clean up the limescale build-up in the heat exchanger.

Specific limescale cleaning chemicals are also available in the market, which offer immediate and effective cleaning.

4. Error Code 05

Error Code 05

The error “05” occurs when the system detects an issue with the combustion. Error code 05 is an imperfect combustion alarm.

A blockage triggers the issue in combustion to the Vent Exhaust. It may also be due to an issue with the Air Intake.


To troubleshoot this error, you must check the vent pipes and remove anything obstructing the air intake or any pipeline leading to the exhaust vent.

5. Error Code 10

Error Code 10

Error code “10” appears when the system has detected a false flame. A false flame may be due to any obstruction or poor material used during installation.


Check out all the vents, flue inlet, heat exchanger, and exhaust termination. Make sure that they are not blocked anyway and have adequate clearance space. You may get a professional service for this purpose.

6. Error Code 11

Error Code 11

Rheem tankless water heater displays error code “11” when the ignition has failed. Several reasons cause ignition failure.


To remove this error, the first step is to check the gas flow to the unit. If the gas connection is perfect and gives the required amount of pressure, but there is still no ignition, look for a service member.

Also, make sure the ignitor is functional before calling for service.

7. Error Code 12

Error Code 12

When you see error code “12” on your Rheem tankless heater, it indicates flame failure.


Ensure all gas valves are open and the gas reaches the heater. You must also ensure that the flame rod does not contain carbon build-up. Again, you can contact a technician to handle this error.

8. Error Code 16

Error Code 16

The error code “16” display indicates an over-temperature warning when the outlet temperature exceeds the remote thermostat setting.


Look for any obstruction or blockage in the heat exchanger. Make sure that there is no airflow restriction to the unit.

Also, check out the vent terminal, outlet thermistor, heat exchanger thermistor, and gas valve.

9. Error Code 21

Error Code 21

The error code “21” occurs when there is a malfunction in the air intake filter switch.


Ensure the correct installation of the front panel. Plus, determine whether the air filter door is seated properly.

10. Error Code 24

Error Code 24

The error code “24” flashes on the display unit when a switch malfunction occurs.


Start troubleshooting this error by shutting off the water and disconnecting the remote control. Next, make sure that the tankless heater is properly grounded.

Press the max and min buttons on the control board to reset the heater.

11. Error Code 29

Error Code 29

If you receive an error code “29”, know that the heat exchanger’s temperature has become too low.


When you see this error code, clean up the air inlet screen and the fins on the heat exchanger.

12. Error Code 31

Error Code 31

When there is a fault in the water inlet temperature sensor, your Rheem heater will display an error code “31”.


You can start resetting this error by inspecting the thermistor wiring for any damage. Also, check for any limescale build-up on the thermistor. Give it a clean if required.

13. Error Code 34

Error Code 34

An error code “34” comes on the display unit when the system detects a fault in the combustion air temperature sensor.


Inspect the ambient thermistor and look for any damage in the wiring. Make sure to remove blockages, if any.

Tightly fit the fan blade on the motor shaft so that it spins freely. Replace the sensor if needed.

14. Error Code 51

Error Code 51

The error code “51” comes when there is some problem with the gas control valve.


To correct this error, your best bet is to contact a professional and get the loose or damaged terminals fixed on the gas control valve wiring.

15. Error Code 61

Error Code 61

If your device’s combustion fan fails, you will see an error code “61” on the front panel.


Ensure there is no problem with the fan motor and that it is turning freely. Even if there is a small restriction, remove it early.

16. Error Code 65

Error Code 65

You will notice an error code “65” when there is some issue with the water control valve.


Look for loose or damaged wiring connections on the water control valve. Ensure the water control valve has the proper voltage.

Call a repair technician to handle this task for you.

17. Error Code 66

Error Code 66

An error code “66” will appear when there is some problem with the water bypass valve.


Call a plumber technician if any damaged wire on the water bypass valve and repair is needed.

Also, ensure that the water by-pass solenoid has the proper voltage it needs.

18. Error Code 71

Error Code 71

The error “71” indicates a fault in the gas inlet valve control.


Ensure no wire is loose or damaged on the gas control valve. Moreover, reach out to a professional assistant to do any repairs.


Rheem tankless water heater is one of the most used household appliances. It comes in different types of models that you can select based on your requirements.

These tankless heaters have an in-built capacity to display an error code when something is wrong within the system. You can better remove the error when you know what each code means.

Hiring a professional service for this purpose is the most appropriate step that one can take.

Frequently Asked Questions

Why Does Rheem’s Tankless Water Heater Display an Error Code?

A Rheem water heater has an in-built diagnostic system. Whenever the water heater detects a problem, an error code in the LED display comes on the front panel.

This code indicates a potential fault in the system. To continue the smooth functioning of the heater, the error must be identified and removed.

If this is not done, an error code will keep appearing, and you may not be able to use the tankless heater.

What Is an Alternative Method To Reboot the Rheem Tankless Water Heater?

While using Rheem tankless heater, you may come across different error codes. You can detect the possible diagnostic problem and its solution by identifying the error.

You can also reboot your Rheem tankless heater with an alternative option that rectifies the error. First, unplug the water heater from the power supply. Allow it to rest for a couple of minutes.

Then plug it back. The error may have been resolved. If not, go for other rebooting options.

What Are Hard Lockout and Soft Lockout in Rheem Tankless Water Heater?

Rheem tankless heater puts the diagnosed problem into two categories, i.e., soft lockout and hard lockout.

A hard lockout indicates a serious situation like ignition, flame, or condensate problem. At the same time, a soft lockout is not an indication of something serious.

Whether a lockout is hard or soft depends on the severity of the error and the underlying problem.

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