Rheem Tankless Water Heater Code 11 (Fixed)

Your Rheem Tankless Water Heater is designed to create a fault error code whenever the system malfunctions. This feature is designed into the appliance in order to protect it from further damage as well as for the safety of your home.

Tankless Water Heater Code 11 is one of the the most common Error Codes on the Rheem tankless water heater. This fault code is also common on Rinnai and Richmond tankless systems.

One of the few downsides of using a tankless system is that when a fault code occurs, there is no way to get any hot water. With a tank system, you are still able to get some warm water for a period.

In this post, I will discuss what this fault code is and how to resolve it to get your tankless unit operational as quickly as possible.

What is Rheem Tankless Water Heater Code 11

Code 11 means that the ignition system has failed. This can happen when there is insufficient gas supply to the tankless unit or a faulty ignitor coil. Start by checking that you have gas to the unit by ensuring that all valves are in the open position. Once confirmed, replace the faulty ignitor coil.

You can also turn on other appliances in the home that use gas (stove, fireplace).

Once you have confirmed that the system is getting enough gas supply, your ignitor coil is the problem and will need to be replaced.

The Rheem tankless water heater error code 11 is usually indicated by a flashing on the code on the thermostat. This flashing is usually accompanied by a high pitched beeping sound. It is important to not the this sound is not a temperature warning.

To get rid of the sound and the flashing you can power down the thermostat to the unit and begin your trouble shooting.

How to Fix Rheem Tankless Water Heater Code 11

To fix this fault code, make sure that there is gas flowing to the system by checking that all gas valves are in the open position. Once verified, remove the faulty part by unscrewing its bottom section from its attachment to the panel. Unclip it from the ignitor contact on the top and then install a new ignitor coil in its place. ignitor coil

Here are the steps of the process in Detail

Step 1: Remove the Front Panel of the Rheem Tankless Water Heater Unit

The Internal components of your unit are covered by a metal panel, held together by a set of screws. Remove the screws to expose the internal parts of the unit. Make sure there is no visible damage to any of the parts.

Step 2: Shut off Power to the Unit

Every tankless unit is powered by electricity even if it uses gas for heating. Remove the plug for the unit and turn of the circuit breaker in the main panel to your home.

You will be able to tell that the power source is completely turned off because there will be no air coming out of the exhaust vents on the top of the unit.

Step 3: Shut off Water and Drain the Unit

Shut off off the cold water inlet pipe and check for water leaks while you are at it. Drain the water heater by relieving it through the vent pipe.

Step 4: Check that there is Gas supply to the unit

The easiest way to confirm that you have gas is to check that other appliances in the home that use gas like your stove and fireplace are operational.

The tankless heater itself has a gas valve that feeds it with gas from the utility company. The valve will have a red handle that controls flow. Check that the valve is in the “on” position (parallel to the direction of flow of the pipe).

Step 5: Replace Ignitor Coil

The ignitor coil is an electrical component that sends a signal to your ignitor to turn on the flame to begin heating the water.

Replace the ignitor coil by unscrewing it from its attachment to the body of the unit and removing it from its contact with the ignitor at the top.

Install the new ignitor coil in place of the faulty one.

Step 6: Power Up The Unit

Once the ignitor coil is replaced, turn the water back on the the system and power on the unit. Don’t forget to make sure that the thermostat is on as well.

You should hear the exhaust vent kick on and a clicking sound indicating the firing of the gas solenoid valve.

Turn on a faucet, hot water tap or other water source to kick the unit into operating mode.

Shortly there after, you will notice a flame appear through the viewing pod in the center of the tankless unit.

Your Water heater is Operational again.

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Causes of Rheem Tankless Error Code 11

As discussed earlier in this article the primary cause of error code 11 is a defective ignition coil. But let’s dig a little deeper into the part to understand why it may fail.

Low Gas Pressure

Ignition Failure can also be the result of low gas pressure on your unit. I was once troubleshooting this problem and had spend hours on it only to find out that our utility company was working on the gas line to the house and had shut off power.

That is the first place to start.

Defective Flame Rod Wiring

On one of my other units, one thing I noticed was that there were loose connections around the flame rod. It showed up on the controls as error code 11.

All I had to do was to remove the flame rod, remove or the dark carbon deposits, reinstall it and then the unit was back up and running.

Bad Ignitor Wire Support

Another often overlooked issue with error code 11 is that the problem might actually be that the Igniter wire harness may be worn out. Unfortunately, it is not worth it it just fix the wiring. You ultimately will be better served by replacing the Ignitor Coil.

Bad Venting Adapter

Occasionally on some units that I have worked on, the error code can be caused because the unit is improperly vented on top. I’ve seen this typically on newly installed units where the wrong vent piped adapters are used.

Depending on your unit, you may have a 3 inch or 5 inch vent pipe and it is important that the adapter at the top of the unit is the same size as well. Check your manual that the correct size vent pipe was used. 

Most will fall into the the range above. 

Rheem Tankless Water Heater Ignitor Location

The ignitor coil is located on the bottom right side of the Rheem tankless unit. Open the front panel by removing the screws around the unit. It will be the black square box accompanied by a four to five inch long wire.

How To Check Ignitor on Rheem Tankless Hot Water Heater

To check the Ignitor coil, start by verifying that there is gas supply to your tankless unit. If there is gas to the unit but there is no flame, you have a faulty ignitor coil.

Reset Rheem Tankless Water Heater

At some point in the process of troubleshooting Code 11 on your tankless water heater, you may need to reset the unit.

Here are the steps

  1. Shut off power to your unit at the circuit breaker 
  2. Open the front of the tankless water heater unit by loosening the screws on the front 
  3. Find the reset button on the inside of the panel
  4. Hold it down and release it.
  5. Close the panel and power the unit back on 

Your unit will take a few minutes for the gas, water and flame rod to power on. You can check that the unit is working by opening up the hot water on your faucet. 

The hot water should begin to run within 15 minutes.


Rheem Tankless Water Heater Systems are generally reliable. But one of the most common error codes they have is Code 11.

Code 11 occurs when there is an ignition failure on the unit. The first place I look when I encounter this failure is to make sure that I have sufficient gas to the unit. If I do, then the next place I look is to replace the ignition coil. 

In 99% of the units I have worked on this fixes the problem.