Rheem tankless water heaters are known for their efficiency and reliability, but encountering error code 11 can be frustrating. This code 11 indicates an ignition failure,( you can notice that no flame in the burning chamber through the burner sight glass) and there are several reasons why it may occur. In this comprehensive guide, we will explore the possible causes of Code 11 and provide step-by-step solutions to help you resolve the issue and restore your hot water supply.

rheem water heater error code 11 from user manual

How To Fix Rheem Tankless Water Heater Code 11: The Reasons & Solutions

1. Insufficient or Restricted Gas Flow

The first thing to check when you encounter Code 11 on your Rheem water heater is the gas supply. Ensure that your propane or gas tank has enough fuel to operate the water heater. Lift the tank to gauge its weight; if it feels light, it may be empty.

gas valve open condition and close condition

Next, verify that the gas is flowing to the burner by checking the gas valve. Ensure the red gas valve is aligned parallel with the pipe to allow gas flow. If you suspect the gas valve is damaged or worn out, consider replacing it.

Related article: Rheem tankless water heater maintenance: Cleaning and Flushing

2. Defective Gas Solenoid Valves

When encountering the dreaded error code 11 on your tankless water heater, one of the potential culprits could be faulty gas solenoid valves. These essential valves play a crucial role in regulating the flow of gas to the main burner for ignition. If the main burner fails to ignite despite the igniter and fan functioning correctly, it indicates an issue with one of the gas solenoid valves.

To diagnose the problem and identify which solenoid valve is causing the issue, a voltage and resistance check is necessary. Here’s how to perform the diagnostic procedure step by step:

rheem tankless water heater gas solenoid valves wiring diagram

The above image shows the PCB wiring with Solenoid valves circuit diagram for Rheem RTG and RTGH tankless water heaters. The highlighted part is for solenoid valves and their wire colors. If you are using different model check its user manual for its circuit diagram.

  1. Check Voltage of Gas Inlet Solenoid Valve #0: The gas inlet solenoid valve #0 should have a voltage reading between 90-120 VDC (Volts Direct Current). To measure the voltage, locate connector D and put multimeter points on Black and Yellow wires on the Printed Circuit Board (PCB) and take the reading.
  2. Check Voltage of Gas Inlet Solenoid Valve #1: Similarly, check the voltage of solenoid valve #1 by measuring the voltage between the Black and Gray wires. The voltage reading should again be between 90-120 VDC.
  3. Check Voltage of Gas Inlet Solenoid Valve #2: Proceed to measure the voltage of solenoid valve #2. Find connector D and put the multimeter points on Black and Blue wires and record the voltage reading, which should be in the range of 90-120 VDC.
  4. Check Voltage of Gas Inlet Solenoid Valve #3: Lastly, measure the voltage output of gas inlet solenoid valve #3 by checking connector D between the Black and Red wires. The voltage reading should fall between 90-120 VDC.
  5. Check Voltage of Gas Inlet Solenoid Valve #4: Lastly, measure the voltage output of gas inlet solenoid valve #4 by checking connector D between the Black and White wires. The voltage reading should fall between 90-120 VDC.
  6. Verify Resistance of Gas Solenoid Valves: In addition to voltage checks, it’s essential to examine the resistance of each solenoid valve. Use a multimeter to measure the resistance of each valve. The resistance of each solenoid valve should read between 0.8 to 2.4K Ohms (Kiloohms).

How To Fix:

If any of the gas inlet solenoid valves do not have the proper voltage reading or show signs of malfunction, it is best to replace the Printed Circuit Board (PCB). Since this task requires technical expertise, it is recommended to seek assistance from a qualified professional to ensure the replacement is done correctly and safely.

Similarly, if the gas solenoid valves show inaccurate resistance readings, the gas control assembly should be changed. If both the voltage and resistance are between the regular values, the issue would be with the main burner. Check the main burner, if it looks

Remember, when dealing with complex components like gas solenoid valves and PCBs, it is crucial to prioritize safety and seek professional help if you are unsure about handling the repairs on your own. Following the correct diagnosis and repair procedures will help clear error code 11 and restore your tankless water heater to smooth operation.

Related: Rheem water heater pilot light won’t stay lit [easy fix]

3. Damaged Igniter Wire Harness

rheem tankless water heater ignitor coil replacement and its location

So, sometimes when your Rheem tankless water heater shows error code 11, it could be because of a damaged igniter wire. Don’t worry, it’s actually quite common. The wiring of the igniter can get cracked or damaged due to wear and tear. If the wiring gets damaged, the ignitor wont work.

To fix this issue, you’ll need to visually inspect the igniter wiring. Just remove the burner cover and take a look at the wire harness. If you notice any signs of wear or damage, it’s time to repair the wiring. Now, if you’re not really into electronics, no problem! Just give a professional electrician a call and they can replace the wiring for you.

4. Defective Igniter

rheem tankless water heater ignitor and burner sight glass location

If the previous troubleshooting steps didn’t resolve the issue, it’s possible that you have a faulty ignitor. The ignitor is a small component responsible for sparking and igniting the flame that heats the water.

To check if the ignitor is functioning correctly, first, ensure that the fan is running. If the fan is operational but the ignitor doesn’t spark, you can perform a voltage test on the ignitor during ignition. To do this, cycle your water heater to initiate the ignition process and then measure the voltage across the connector wires of the ignitor. The normal voltage range should be between 109 to 132 VAC (Volts Alternating Current). If there is not voltage comming from the power control board to the ignitor, we need to replace the whole PCB.

If the voltage is in the above range, takeout the ignitor and visually inspect for carbon buildups, or dirt, if possible try to clean it with low grit sand paper, if it looks damaged you need to replace the ignitor by following the below steps.

How to replace the ignitor

When dealing with your Rheem tankless water heater’s igniter coil replacement, it’s essential to follow a few simple steps. First, ensure your safety by unplugging the power cord and turning off the gas valve, inlet water, and circuit breaker.

To begin the process, you’ll need to drain the water from the heater. This can be done by opening the relief valve, allowing the water to drain out.

Next, locate the igniter coil, which can be identified by its part number, RTG20235C. Remove the screw that holds it in place and carefully follow the igniter wiring to pull out the plastic insert. This will allow you to remove the old igniter coil from its position.

Now, it’s time to introduce the new igniter coil, which should also be part number RTG20235C. Carefully install it in place of the old one, ensuring it fits snugly.

To complete the installation, secure the new igniter coil by screwing it into position. Don’t forget to put the plastic insert back where it belongs, securing it properly.

5. Verify the Ventilation

Inspect the venting system for any obstructions that may hinder airflow. Clear away debris or nests that could block the ventilation which effect the combustion process.

By following these steps, you can troubleshoot and resolve Code 11 on your Rheem tankless water heater. Remember to prioritize safety and seek professional assistance if needed. With proper maintenance and care, your Rheem tankless water heater will continue to provide you with reliable hot water for years to come.

Related article: Rheem water heater leaking from bottom or top


Code 11 on your Rheem tankless water heater indicates ignition failure. Follow our troubleshooting steps to identify the cause and resolve the issue. If you have further questions or need assistance, feel free to leave a comment below. We are here to help you get your hot water supply back up and running.

Link to user manual : here

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