Rheem Tankless Water Heater Code 11 [Reasons + Solutions]

Rheem tankless water heater code 11 is the error indication of the ignition failure or no ignition in the unit. The major reasons for popping up Rheem code 11 include insufficient gas supply, power outage, and defective igniter. 

rheem tankless water heater code 11

Plus, clogged burner assembly, high-limit switch failure, defective gas solenoid valves, and poor airflow are also responsible for ignition failure.  

If the error message 11 displays on the control panel, first, ensure a proper gas supply to your water heater. Once confirmed, check and replace the faulty igniter coil. 

Stay tuned to this comprehensive article till the end to get a well-proven guide for the ignition failure issue

Quick Solution

Before heading over to the detailed troubleshooting guide, let’s glance at the table below highlighting all the probable reasons and a quick fix for Rheem tankless code 11.

Probable ReasonsPossible Solutions
Insufficient gas pressureEnsure there is gas in your heater unit. Make sure the gas type and pressure are correct. Bleed all air from gas lines. Contact the local gas station

Power outage

Check the circuit breaker is “ON” position. Ensure that the water heater is properly grounded
Non-operational Igniter Ensure a  secured wire connection of the igniter. Replace the worn-out igniter coil
Clogged burnerInspect & clean the burner assembly
High-limit switch failureReset the heater Replace the tripped high-limit switch
Defective gas solenoid valvesReplace the faulty gas valve assembly
Poor airflowClean the air filter clean out the heater venting system

How To Fix Rheem Tankless Water Heater Code 11

In this guide, we will disclose each of the responsive factors behind Rheem error 11 with corresponding effective solution procedures in detail. So, without further ado, let’s start.

1. Insufficient Gas Pressure

If error code 11 is popping up on the control panel of your water heater, it is certain that interruptions in the gas supply are the root culprit. 

insufficient gas pressure

To ensure a fluent operation in the tankless water heater, the minimum inlet gas pressure should be between 5.0″ W.C for natural gas and 13.0″ W.C (1.25 to 3.24kPa) for LP gas. 

When the gas pressure becomes less than the recommended amount, the heater catches several errors, including ignition failure. The major reasons for insufficient gas pressure include:

  • Air in the gas line
  • The gas line, meter, and regulator are not sized 
  • The gas valve is closed
  • Clogged or kinked hose 
  • Not enough gas in the tank


To troubleshoot the problem, here are a few things you could check:

  • First, check the gas valve to see if it is turned on. There is a red handle on the valve, which controls the gas flow. Make sure it is in the “on” position.
  • If there is air in the gas line, bleed the air from the line. Make sure the gas line, meter, and regulator are sized properly.
  • If the gas hose is clogged, wash away the gas hose with soapy water. Also,  straighten the kinked hose. 
  • Now check whether the gas issue is also occurring to other appliances like the stove or fireplace. If yes, contact your local gas station.

2. Power Outage

If your electric Rheem tankless water heater is experiencing ignition failure, the power outage might be the leading reason for this issue. Even if you are using a gas tankless water heater, it is powered by electricity. 

So in the case of no ignition, there is a higher chance either the plug for the unit is damaged or the tripping circuit breaker. At times, loose wiring connections lead to this issue.


  • First up, look for the circuit breaker for your tankless water heater, and make sure it is in the “On’ position.
  • Check the wiring connection of the water heater and ensure all are in well working condition. Also, ensure that the water heater is properly grounded.
  • Press the power on/off button and turn off the water heater. Wait for 5 minutes and turn the water back on.
  • If the circuit breaker continues to trip, call an electrician. 

3. Defective Igniter

The non-operational igniter is another major reason for popping up the error code 11 on your tankless water heater. The main function of the igniter is to ignite the gas when the gas valve is open. 

defective igniter

If there is no ignition in your water heater, there is a higher possibility of a defective igniter system. After long usage, the igniter might be defective. 

Here, either the igniter wiring is damaged or the igniter coil. The igniter coil is an essential electric component of the igniter. Anyway, due to excessive wear and tear, the coil might be damaged, interrupting the ignition system.

In case of this, the only solution is to replace the igniter of your tankless water heater. Many of us get confused about the Rheem tankless water heater igniter location. 

Here are the needed instructions to locate the Rheem igniter and the replacing processes:

How To Replace Igniter On Rheem Tankless Water Heater

First, turn off the power supply to the water heater and also shut off the gas supply. Then, unscrew the attached screws around the unit and detach the front panel. 

Now, look for the igniter assembly inside the system. First, locate the igniter coil. You will find it on the bottom right side of the inside unit.

Unplug the igniter coil wire plug from the cable connection that is secured in rubber. Then, remove the screws of the ignition coil that keep it in place. Next, pull the coil from the cable and remove it. 

Take the new igniter coil and place it in the igniter assembly.

Connect the igniter coil with the cable. Then, attach the igniter coil wire to the connection and put the plastic insert back into its place. Screw the igniter coil in the right place and complete the installation.

4. Clogged Burner

If your tankless water heater fails to ignite, clogged burners are the major reason for this issue. After extended usage and improper maintenance, the burner assembly of the heater can be blocked by carbon or condensate build-up. 

clogged burner

Debris and carbon build-up prevent the burner from firing up and lead to ignition failure error. Also, if the burner plates are not properly seated in the assembly, it could be one of the responsive factors that failed ignition.

How To Clean Burner On Rheem Tankless Water Heater

Follow the below step-by-step guide to inspect and clean the burner assembly effectively:

i). Initial Disassembly:

Turn OFF the electrical power and gas supply to the water heater. Let the tankless water heater cool. Remove the front panel to expose the internal parts of the unit.

ii). Inspect The Burner:

Detach the printed circuit board and let it hang. Then remove the gas line clips and pull the gas pipes out. 

Also, remove the igniter plate and the door switch. After that, disconnect the burner cover plate. Pull out the burner slightly by unscrewing the screws that hold it in lace. 

iii). Clean The Burner Assembly:

Detach the fuel rails from the assembly and clean them by blowing with compressed air. You can use a little wire for better cleaning. 

Now take fine sandpaper of 100 grit and rub the flame rod. Use compressed air to blow back down through all the burner ribbons. After cleaning, ensure all burners are properly seated.

5. High-limit Switch Failure

High-limit switch failure is one of the leading reasons for interruption in the ignition system of the water heater. Basically, the high-limit switch acts as a safety device in the water heater, which prevents the water from becoming too hot. 

high-limit switch

When the high-limit switch trips, the heater unit constantly turns off and stops the ignition process.


In case of tripped high limit switch, set the temperature control lower.

Turn off the water heater and then turn it back on after a few minutes. If that fails to fix the problem, the high-limit switch needs replacement.

6. Defective Gas Solenoid Valves

A faulty gas solenoid valve is one of the most common reasons for leading your Rheem tankless water heater to ignition failure. Gas solenoid valves are used to control the flow of gas in the water heater by opening and closing. 

gas solenoid valves

So, if the main burner of your water heater not igniting, or if the heater ignites but keeps going out, it’s sure that the gas valves are faulty. Either the gas valve has a short circuit or experiencing an incorrect voltage supply.


Take a voltage meter and check the voltage reading for each of the inlet solenoid valves. A well-working gas valve will give a reading of 90-120 VDC. 

Also, measure the resistance of these solenoid valves, which should be 0.8 to 2.4K Ohms. 

If the voltage of any of the inlet valves is out of range, you need to replace the valve. It will be better to contact a professional to do this task for you.

7. Blocked Air Vents

Poor airflow is a frequent cause of ignition failure. All tankless water heaters must be vented vertically to get the combustion gases out. If not, exhaust gas recirculate in the heater and causes incomplete combustion. 

blocked air vents

In case of poor airflow in the water heater, the most probable reason is the blocked air inlet filter. Also, loose wiring connections and bent or obstructed vents can be the reason.


Cleaning the air intake filter is quite simple. First, you need to turn off the unit and disconnect the power connection. Now, remove the cover plate to expose the internal parts. 

Locate the air filter from the top inside and remove it by disconnecting a single screw holding it. The air filter will look like the below picture:

Once removed, clean it using mild detergent and a soft brush. Then rinse the air filter. Also, inspect the venting of the heater to clean the carbon residue build-up from it. Hire a certified plumber to handle the tasks. 

How To Reset Rheem Tankless Water Heater

While operating the water heater, you may need to reset the system for various purposes. But many of us get confused about how to reset a tankless water heater. 

rheem tankless water heater

Resetting the Rheem tankless water heater is a very straightforward process. Follow the step-by-step instructions for resetting your water heater.

  • First, move to the electric panel of your water heater and locate the water heater circuit. Set the circuit to the On position if it gets flipped to the Off position.
  • Then remove the control panel cover and locate the reset button. You will find it behind the insulation.
  • Press and hold the reset button until you hear the click sound. Then release it. Reconnect the gas valve if it is disconnected. 
  • Replace the control panel cover, and that’s all you have done. You have reset your Rheem tankless water heater.


Why is my Rheem tankless water heater not working after a power outage?

If your Rheem tankless water heater not working after a power outage, be sure either there is damaged wiring, or the circuit breaker gets tripped. A defective thermostat, switchboard, or bad heating element can also be the culprit. 

Why does My Rheem water heater keep turning off?

Your Rheem tankless water heater won’t stay on mainly due to tripped high limit switch or the circuit breaker. Also, a defective flow sensor fails to send a message to the control board for heating water, and the heater shuts off.

Bottom Lines

Well!! That’s all we have about Rheem tankless code 11 in this troubleshooting guide. We hope it was an easy read for you to learn about all the responsive factors for occurring the Rheem code 11. 

Upon following this guide, it will be easy for you to erase such errors from your tankless water heater. Still, if you face any troubles, don’t be late to let us know through comments. We are always here for you.

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.

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