Rheem Tankless Water Heater Code E5 [Reasons + Solutions]

Rheem Tankless water heater code E5 is a diagnostic alarm from the control panel. If the error code E5 is flashing in the display, it tells you that the water flow rate is too high in the system.  

Plus, incomplete combustion is another reason responsible for appearing the code. The tankless water heater will encounter a problem in the combustion system due to a blocked air filter, or from the blockage in the heater venting. 

rheem tankless water heater

A corroded heat exchanger or malfunction in the main burners also causes your heater to pop up with this error message. Continue reading our following comprehensive guide to getting rid of the error code ASAP.

What Does The E5 Code Mean On A Rheem Tankless Water Heater

The E5 error code on a Rheem Tankless Water Heater signifies the excessive water flow rate. That means the water volume of the system is exceeding the recommended rate and that’s the reason the heater is failing to reach the desired preset temperature. Slowing down the water flow rate will be enough to resolve the issue.

But there are a few more factors that need your attention. Before beginning the main discussion, let’s glance at the below table, highlighting all the probable reasons with instance solutions:

Probable ReasonsPossible Solutions
Too much water pressure> Adjust the water pressure regulator of the main water line.
Malfunction in the combustion system> Clean the air intake filter.
> Inspect the air intake vent and exhaust outlet for clogs. > Make sure the condensation trap is blockage-free and installed properly
Corrosion build-up in the heat exchanger> Clean or replace the corroded heat exchanger.
Defective combustion fan motor> Replace the faulty fan motor.
Problem with the main burner> Inspect the burner assembly and blow down the dirt using compressed air.
> Ensure the burner ribbons are seated properly.

How To Fix Rheem Tankless Water Heater Code E5 [5 Easy Solutions]

Now take an in-depth look at the step-by-step guide to fix the Rheem tankless water heater code E5 in a shorter time.

Note: You can also read how to fix Rheem water heater 6 3 flashes.

1. Water Flow Is Too High

As you have read above, the error code E5 in your tankless water heater is a clear indication of the excessive water flow in the heater. When there is too much water pressure, it will not let the water absorb heat. 

Besides, the temperature can’t able to reach the set temperature. That’s the reason the LED control board will show an E5 error code.

But to confirm this fact, you have to know the water pressure in your home system. The process is quite simple, and you just need a water pressure gauge. Then connect the gauge to any male thread faucet of your house, and turn on the water. Now measure the water pressure.

In general, the standard residential water pressure range should be between 40-60 psi (pounds per square inch). But in case the water pressure reaches above 80 PSI, be sure it is definitely time to lower the water pressure. 

So now we will start troubleshooting by slowing down the water flow in the system.

How To Adjust High Water Pressure

Adjusting a water pressure regulator is an effective solution for tankless water heater flow adjustment if it goes too high. It is the most common plumbing valve installed in the water line of your house. 

adjust high water pressure

If you have one installed regulator in your house water pipe and encounter a high water pressure issue, chances are it needs to be adjusted. 

Follow the below instruction to adjust the regulator:

  • First off, locate and turn the water valve to the off position. You will find a screw or bolt and a locking nut system in the regulator. Loosen the locknut using a wrench by turning it counter-clockwise.
  • Before tightening the locknut, re-test the system pressure using a pressure gauge. If it shows the recommended pressure, secure the lock nut tightly. Finally, turn the main water valve back on.

2. Malfunction In Combustion System

According to Rheem tankless water heater, the error code E5 will pop up when there is a malfunction in the combustion system. That means there is an issue with either combustion air or venting.

To continue the heater operation, the system needs fluent airflow to remove the combustion gas. Lack of combustion air is one of the most frequent reasons for throwing the error E5 on the control panel. 

Anyway, there are some major reasons why the unit is not able to vent or combust air properly. That includes:

  • Blocked air filter
  • Clogged condensate trap
  • Blockage in the air intake and exhaust vents
  • Incorrect installation of the condensate
  • Improper vent length

In this troubleshooting stage, you need to visually inspect the venting systems of the water heater and check the condition.


Follow the below step-by-step guide to fix the combustion issue from your water heater:

Step 1: Clean The Air Intake Filter

Whenever you encounter a combustion problem in your tankless water heater, making the air filter blockage free is a must to fix the issue. 

Before starting the cleaning, make sure you have turned off your water heater and disconnected it from the power connection. 

Then remove the front cover of your heater to inspect the internal parts. Locate the air filter from the top right side of the heater. If you are confused, see the picture below:

rheem tankless water heater air filter

Take the air filter out from the filter adapter and clean it using a toothbrush. Once done, rinse the loose debris under the running water. Then use a towel to dry off the filter. Re-install the air filter back into place

Step 2: Clean The Exhaust Vent Pipe & The Condensate Trap

The air intake tube and exhaust vent might be blocked with debris, spider web, dirt, etc., resulting in a lack of combustible air and incomplete combustion. So, it is time to time to clean the venting following the below ways. 

  • Inspect the air intake pipe and exhaust outlet of your water heater. You will find dirt, debris, and carbon buildups, creating problems in combustion. Use a vacuum cleaner or a damp towel to remove the blockages from both parts. 
  • Now come to the condensate trap and look for any degradation. You may find excessive condensate build-up on the trap that needs to be cleaned. After cleaning, ensure a proper installation of the venting system.   

3. Corroded Heat Exchanger

Corrosion or scale buildup in the heat exchanger is the leading reason in case of error code E5 in the Rheem tankless water heater. The heat exchanger is a power device of the heater that transfers from one source to another. 

rheem tankless water heater heat exchanger

Due to wear and tear, corrosion build-up, and constant expansion lessen its efficiency and prevent the system from operating at its energy-efficient state. 

Plus, a cracked or corroded heat exchanger is one of the major reasons for system overheating due to poor venting and combustion. 


In case of corroded heat, you may have to clean the heat exchanger to dissolve the Calcium Carbonate deposits. Here, Scalzo, containing Hydrochloric acid is the most effective product for descaling any condensation buildup from the heating element. 

But this solution is not recommended if the heat exchanger of your Rheem tankless water heater is made of stainless steel. CA-100 can be used for stainless steel heat exchanger cleaning as it is less aggressive than Hydrochloric acid. So, there will be no chance of pitting the stainless steel.

Contact a professional to clean or replace the heat exchanger effectively.

4. Faulty Fan Motor

If still, the error E5 is displaying on the heater control panel, it is sure the faulty fan motor is now to be blamed. 

rheem tankless water heater faulty fan motor

Basically, if you have a power vent tankless water, it uses a blower or fan to continue the combustion operation. It is an essential element of the water heater system, which exhausts the combustion gas and removes excess heat through the exhaust venting. 

The blower runs through a motor and if it goes bad, there’ll be no airflow at all. That means a bad motor is interrupting the combustion system, leading to the error E5. 


To check the blower motor, first, locate it from behind the printed circuit board (PCB) inside of the heater, indicated in the below picture. In this case, you need to inspect the fan motor and check whether it is operational and in good working condition. 

Replace the non-operation fan motor. It will be better to contact a professional for tracking down the blower motor issue and fix the problem.

5. Problem With The Main Burner

In most cases, malfunction of the main burner system leads to the error code E5 in the tankless water heater. Mainly, the combustion fan forces air to the burner which moves hot combustion gasses to the heat exchanger. Then the heat exchanger transfers heat from the burner into the water quickly.

rheem tankless water heater main burner

Now if the burner assembly is blocked by dust and debris, it will fail to continue its operation, leading to interruption in the combustion system. Then, as a diagnostic alarm, the control panel displays the error code E5. 


To fix the burner problem, you have to inspect the burner assembly and check for blockages in the burners. Clean the burner assembly. Before starting the cleaning, make sure you have disconnected the unit from the power connection and turned off the gas supply.

Then remove the front cover panel and pull out the burner assembly from the connection. Clean the burner ribbons using compressed air. Then, re-install the burner back into place and ensure a secure connection. 

How Do I Clear The Error Code E5 On A Rheem Tankless Water Heater

Once you have done all the above attempts and fixed the error code E5 issue, it is time to clear out the error code. Reset your Rheem tankless water heater unit will assist you in clearing the error code from the control panel. In this instance, follow the below instructions:

  • First of all, press the power button to clear the hard lockout.
  • If that doesn’t work, there is an alternative option to rectify the error. Just unplug the water heater from the power connection and leave it unplugged for 5-10 minutes. Then plug it back in. This will reboot your water heater and clear the error from the control panel display. 


How Do You Fix Code 11 On A Rheem Tankless Water Heater?

Rheem tankless water heater Error code 11 is the error indication of the ignition failure. Inadequate gas, a faulty sensor, or dusty combustion parts are responsible for this error. You need to clean the combustion parts and make sure that the igniter is functional. 

What Does E4 Mean On A Rheem Tankless Water Heater?

An E4 error code in the Rheem tankless water heater signifies a problem with the water temperature sensor. A faulty flow meter sensor and poor or broken wiring connection to the sensor are responsible for triggering the error code E4.

What Is Code 13 On A Rheem Tankless Water Heater?

Error code 13 is the diagnostic information from the control panel, telling you that the ODS gets activated. Defective ODS thermocouples, dirty or defective flame rods, and incorrect burner manifold pressure are the culprits for popping up this warning message. 

Does My Rheem Water Heater Have A Reset Button?

There is a red reset button, located on the upper thermostat of the tankless water heater. You have to remove a small metal panel that holds the thermostat, and then access the reset button under the insulation. 

Bottom Lines!

Well! We are almost at the endpoint of this article. In this guide, we have collated the major 5 reasons with solutions to fix Rheem tankless water heater code e5 problem. 

We hope this effective guide will have proven well in lessening much effort for searching on the internet to find the solution. Through our guide, expectantly, you have solved this problem very easily.

Still, if you are facing any trouble, then let us know in the comment box. We will try our best to solve the problem ASAP.

About William

William is the founder of Fireplacehubs.com. He has real life practical skills in fixing smoker & heating appliance issues. He loves to share his knowledge & helps others in fixing their appliances & saving their money. William firmly believes that anyone can repair his or her unit with the correct guidance & knowledge. See more at about us.

4 thoughts on “Rheem Tankless Water Heater Code E5 [Reasons + Solutions]”

  1. Tried the reset, even shut down main power for ten minutes. Code E5 is still showing. I also have a problem with the hot water going cold after running for about three minutes. Cold shower not my idea of fun. Unit is about two years old Rheem-36. RTEX-36.

    • Hi Scott

      Mainly E5 on a Rheem tankless water heater means a high water flow rate. It can also mean a bad combustion alarm, a high water flow rate, a motor problem in the water heater or the voltage of the power supply is very low, and a pilot or main burner valve problem. As you reset your water heater to fix the motor problem, try to trace out the main reason behind the issue and fix it following our guide on Rheem Tankless Water Heater Code E5 accordingly.

      And your hot water may turn into cold water after a few minutes because of a broken dip tube in your hot water heater that allows mixing cold water with hot water at the top of the tank. As a result, you get cold or lukewarm water.

      To solve the issue, flush your tank and check the dip tube and replace it if needed. It would be wise to take help from a professional to do the work.

      Hope you will get the solution.


    • Hi Mario

      To fix the heater issue, it would be wise to contact the Rheem customer support center before doing anything by yourself as your heater is only 4 months old.

      Best of luck!


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