Rheem Tankless Water Heater Code 11 [Why + How To Fix]

Rheem tankless water heater code 11 appears when there is an ignition failure. It can be caused by many possible reasons.

rheem tankless water heater code 11

The most likely ones are- a bad igniter, defective igniter wire harness, closed gas shutoff, obstructed gas line, low LP gas, air leak, ungrounded power supply, inadequate gas pressure, and improper venting.

Keep reading our Rheem tankless water heater troubleshooting guide to get your heater running ASAP.

Table Of Contents

Rheem Tankless Water Heater Code 11 [Reasons + Solutions]

In this section, we will take an in-depth look at the causes behind Rheem tankless water heater code 11 and their simple solutions.

rheem tankless water heater

Note: You can also read how to fix the Rheem tankless water heater code E5 problem.

1. Bad Igniter

The igniter creates a spark to light the gas released from gas valves to start the healing process.

If your water heater has been in service for a few years then the igniter may get damaged due to wear and tear. If the igniter fails, the water heater will not turn on.


The only way to fix this issue is to replace the igniter. You can look for a replacement online.

Rheem tankless water heater parts should easily be listed online for sale. Follow these instructions to replace your igniter:  

  • To begin, unplug the power cord. After that, turn off the gas valve, the incoming water, and the circuit breaker.
  • To drain the water from your heater, open the relief valve. 
  • Locate and remove the igniter coil and the screw that holds it in place. Pull and remove the plastic insert by following the igniter wiring. Remove the igniter coil now.
  • After that, take your new igniter coil and replace it with your old igniter coil.
  • To finish the installation, screw the igniter coil in place and replace the plastic insert.

2. Defective Igniter Wire Harness

Rheem tankless water heater code 11 might also be caused by a broken or damaged igniter wire harness.

defective igniter wire harness

Excessive wear and tear may cause damage to the igniter wiring.


Examine the igniter wire for any damage. To inspect the wire harness of your igniter, remove the burner lid. If the wiring shows signs of wear and tear, it needs to be repaired.

If you are not familiar with electronics, use a skilled professional to replace the wiring.

3. Closed Gas Shutoff

A gas shutoff is installed to turn off the gas supply to the water heater. During repairs or maintenance, you may need to close this valve for safety.

closed gas shutoff

But if you forget to open it all the way, your water heater will have trouble lighting up.


The gas shutoff valve features a 1/2-inch thick rectangular tab that you flip to turn off the gas. The valve is open and the gas is on when the tab is parallel to the gas pipe.

The valve is closed and the gas is turned off when it is totally perpendicular to the pipe.

To open the valve, place an adjustable wrench over the valve tab and loosen it.

Clamping pliers or an open-end wrench can also be used. Make the tab fully parallel to the gas line. It should take a quarter-turn.

4. Obstructed Gas Line

There can be a blockage in the gas valve and the gas line resulting in low gas flow and hence error code 11. Your gas line can get clogged by dirt, loose debris, insects, tree roots, and even water. 

obstructed gas line

A gas line, on the other hand, can acquire a bad dent or kink that prevents gas from flowing through it. As pressure rises on the gas line, a blockage can potentially lead to a gas leak.


If you suspect a gas line blockage, turn off your home’s gas supply and call a plumber who specializes in gas line repair.

A professional can figure out the source of a blockage and clean it with special equipment, like a drain auger.

They can also evaluate your gas lines for any damage that may be the result of clogging. For example- a gas leak.

5. Low LP Gas

It could be that your propane tank is running low on gas. Simply lift it up and see if it feels heavy enough.

low lp gas

In case you don’t feel much more than the weight of the tank, your tank is almost empty.


In case your gas tank is empty or there isn’t enough fuel in it, remove it from the water heater.

Take it to the nearest gas station to get filled up. Reattach the snow-filled tank and your heater will be good as new.

6. Air Leak

Air in the gas line can cause ignition failure. It may cause a weak flame or no flame at all. 

air leak


The solution is to bleed the gas line. Here’s how you do it, with a gas water heater model:

  • First, locate the gas valve control knob. Push it in and turn it counterclockwise until the term “Pilot” or “Ignition” appears in the “On” position. It should compress inward a quarter-inch when kept in this position.
  • Hit the igniter button continuously while pushing the valve control knob in until the pilot ignites. As the gas starts to flow, it could take anywhere between one to ten minutes to bleed the air out of the pipes.
  • Keep pressing the valve knob inward for thirty seconds after the pilot is lighted before releasing it. Set the valve to the “On” position now that the pilot light has lit.
  • Redo the entire process if the pilot light goes out. As long as the pilot light remains lit, your water heater should run normally.

7. Ungrounded Power Supply

Without a properly grounded electrical connection to your water heater, not only do you risk getting shocked but it may also cause ignition failure.

ungrounded power supply

Thus, error code 11 appears on your Rheem tankless heater.


You need to hire an electrician to ground your water heater. It is safe to enlist the help of a professional as earthing can be tricky.

8. Inadequate Gas Pressure

Various models may have different minimum gas pressure requirements. Yours can be found on the rating plate on the water heater.

inadequate gas pressure

Every model, however, must have a pressure of 10.5″ w.c. or 2.6 KP for natural gas and 14″ w.c./3.5 kPa for LP gas.

Ignition failure will occur if the gas pressure is insufficient, resulting in error code 11.


A gas pressure regulator is a piece of equipment on your heater. As you can see, it regulates the pressure of the intake of gas. It’ll be at the end of your gas supply pipe.

Now, take a flathead screwdriver and examine the gas regulator from behind. Remove the cap from the regulator’s very center.

Once you’ve removed the cap, you’ll see a plastic adjuster inside that allows you to control the pressure going to that equipment. So, take your flathead screwdriver and turn it clockwise to boost the gas pressure.

Check the flame after two turns to see if it is powerful enough. Increase the number of turns if necessary. To decrease pressure, turn in an anticlockwise direction.

9. Improper Venting

Your water heater model has some specific instructions on venting material, pipe thickness, and configuration.

improper venting

If you don’t meet them, your heater may fail to ignite causing error code 11.


Check the Rheem tankless water heater manual for your specific model. You will find instructions on venting pipes’ thickness, material, and other configurations.

Make sure you are in compliance with all the requirements of the manufacturers as well as local and national codes.

You will need to hire a professional to help you with proper venting installation. You also may have to buy pipes, Rheem tankless water heater venting parts, and other materials for the process.

Watching the video will be helpful for you.


What happens when the exhaust to your water heater is blocked?

Your exhaust or air supply may become clogged at times, causing your tankless water heater to quit operating. Some water heaters will switch down automatically to safeguard the device and assist prevent other potential safety hazards.

Do tankless water heaters get clogged?

Yes. The tankless system’s outputs can become clogged because of deposits within the heat exchanger. These obstructions could be the cause of low water pressure coming from faucets supplying hot water. 

What is code 13 on a Rheem tankless water heater?

It means poor or incomplete combustion. Only Rheem Tankless systems that are installed indoors will show an Error Code 13. Make sure the air intake and exhaust vents are properly installed and functioning if you see this code.

What does code 12 mean on a Rheem tankless water heater?

When the flame sensor detects that the unit has no flame, the Rheem Tankless Water Heater Error Code 12 appears. In preparation for troubleshooting, the system is turned off. Check whether the unit has a gas supply.

Why is my Rheem tankless water heater beeping?

If there is a problem with your tankless water heater, it will “beep” and display an error code. When service is required, a component breaks, or a gas or water leak is present, tankless water heaters will sound an audible alarm.


Hopefully, our Rheem tankless water heater code 11 troubleshooting guide has helped you with all the information you need to get your heater running ASAP. 

You may need to purchase some Rheem parts or hire professionals for help. All of this can be costly.

Try keeping up on your heater’s maintenance to prevent future issues. Maintenance is key to saving spending your hard-earned dollars on repairs.

About David

David is a man who loves doing research and finding out the best solution to any type of heating appliance issues like heaters and fireplaces. Whenever he finds the perfect solutions to any issues of heating appliances after doing in-depth research, he loves to share them with his readers. In fact, his aim is to help his readers to fix the issues with their heating appliances easily.More about us .

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