Fixing Rheem Tankless Water Heater Code 12: Your Ultimate Troubleshooting Guide

If you own a Rheem tankless water heater and have encountered the Rheem tankless water heater code 12 error, you’re not alone. This error, also known as the Flame Failure error, can be frustrating and disruptive to your hot water supply. Understanding the causes of this error and knowing how to troubleshoot it can save you time and money on unnecessary repairs.

In this article, we will guide you step-by-step through the troubleshooting process, helping you identify and resolve the issue causing the Rheem tankless water heater code 12 error. Whether you’re a homeowner or a professional plumber, this comprehensive guide will provide you with the knowledge and tools to reset your Rheem tankless water heater and prevent future errors. Don’t let the Rheem tankless water heater code 12 error leave you in the cold – read on to learn more about resolving this common issue.

The most important facts in a nutshell

  • The Code 12 error in Rheem tankless water heaters is caused by flame failure.
  • Troubleshooting steps include checking the flame sensor, evaluating the gas supply, assessing gas pressure, inspecting gas lines, and checking the venting.
  • A comprehensive guide is provided for resetting the Rheem tankless water heater, along with preventive measures to avoid future Code 12 errors.

rheem tankless water heater code 12

What Causes the Code 12 Error?

The enigmatic Code 12 error , like a riddle from the abyss, haunts the realm of Rheem tankless water heaters, casting a shadow of uncertainty upon their very existence. Its origins, shrouded in mystery, can be traced to a myriad of possible causes. Among them, a flame sensor tainted by the grime of time and neglect, its delicate senses dulled, unable to discern the flicker of life within the heart of the heater.

Or perchance, a gas supply, feeble and inadequate, withholding the fiery essence needed for ignition, leaving the water heater in a state of perpetual darkness. And yet, another foe lurks in the shadows, low gas pressure, silently sabotaging the heater’s endeavor to maintain a steadfast flame, its whispers of inconsistency echoing through the silent halls of hot water deprivation. A call to action, a swift response is paramount, for within lies the key to an efficient and bountiful reign of warmth, ensuring the Rheem tankless water heater fulfills its destiny, bestowing upon us the gift of hot water.

Step 1: Checking the Flame Sensor

In the realm of troubleshooting, if you happen upon a Code 12 error while tending to your trusty Rheem tankless water heater, your first port of call should be the flame sensor. This humble yet pivotal component has been known to shoulder the blame on occasion. By giving the flame sensor a thorough cleaning, you can bid farewell to any dirt or debris that might be causing the conundrum.

This straightforward endeavor often works wonders, alleviating the Code 12 error and restoring your water heater to its former glory. Moreover, take a moment to scrutinize the connections leading to the flame sensor. Confirm they are firmly fastened and free of any damage.

Loosened or compromised connections have the power to impede the sensor’s performance, ushering in the Code 12 error. Should any complications arise with these connections, it may be necessary to acquire a replacement flame sensor. Bear in mind, the flame sensor plays a pivotal role in ensuring the secure operation of your tankless water heater.

Its duty is to detect the presence of a flame, granting the heater permission to proceed. By routinely tending to the cleaning and inspection needs of the flame sensor, you can fend off future Code 12 errors and rest easy knowing your Rheem tankless water heater will serve you dutifully and dependably.

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Troubleshooting Steps Table

Step Number Troubleshooting Step Possible Causes Recommended Actions Result
1 Check the Flame Sensor Dirty or malfunctioning flame sensor Clean or replace the flame sensor according to the manufacturer’s instructions If the flame sensor was dirty or faulty, the code 12 error should be resolved
2 Evaluate the Gas Supply Insufficient or interrupted gas supply Verify gas valve is fully open and check for any gas line obstructions or leaks If there were any issues with the gas supply, resolving them should eliminate the code 12 error
3 Assess Gas Pressure Inadequate gas pressure reaching the unit Measure gas pressure at the unit and ensure it meets the manufacturer’s specifications If gas pressure is below the required level, adjustments or repairs may be necessary to fix the code 12 error
4 Inspect the Gas Lines Damaged or improperly connected gas lines Visually inspect gas lines for any signs of damage or loose connections; repair or replace as needed Fixing any issues with the gas lines should resolve the code 12 error, if present
5 Check the Venting Blocked or improper venting Inspect the venting system for any obstructions or incorrect installation; clear or adjust as necessary Correcting venting issues should eliminate the code 12 error, if it was related to improper venting

Step 2: Evaluating the Gas Supply

Unraveling the enigma of the Code 12 error on your Rheem tankless water heater requires a meticulous investigation. Begin by delving into the gas valve, ensuring its alignment and integrity are intact. Should doubts persist, consult the guidance bestowed upon you by the manufacturer.

Moving forward, scrutinize the gas pressure regulator, the gatekeeper of gas flow into the water heater. A malfunctioning or improperly adjusted regulator could be the culprit behind the Code 12 error. In such cases, seeking the expertise of a professional is highly recommended.

Last but not least, embark on a quest along the gas line, searching for any hindrances obstructing the natural flow of this vital fuel. Unearth any signs of damage or debris and swiftly eliminate any obstructions you may encounter. By meticulously assessing the gas supply, you bestow upon yourself the power to rectify any underlying issues with the gas valve, pressure regulator, or gas line that may be triggering the formidable Code 12 error on your Rheem tankless water heater.

Step 3: Assessing Gas Pressure

In unraveling the enigma of the Code 12 error haunting your Rheem tankless water heater, the first step lies in a meticulous evaluation of the gas pressure. The pressure, you see, holds the key to unlocking the mystery behind this perplexing error. To embark on this journey of discovery, equip yourself with a manometer.

This remarkable device will unveil the secrets of your water heater’s performance by measuring the pressure. Connect the manometer to the gas line, and with bated breath, observe the reading it bestows upon you. Should the gas pressure prove insufficient, fear not, for there is a solution.

Call upon the aid of a seasoned professional, whose expertise shall guide them in making the necessary adjustments. Through their skilled hands, your water heater shall once again sing its soothing song of warmth and comfort. But, dear reader, if the gas pressure dares to soar to dangerous heights, heed my words of caution.

Do not tarry, but hasten to seek the assistance of a qualified technician. Only they possess the knowledge and skill to tame the tempest of high gas pressure and restore harmony to your abode. Remember, dear reader, that assessing the gas pressure is an indispensable step in banishing the Code 12 error from your Rheem tankless water heater.

Arm yourself with a manometer, make adjustments if required, or summon the aid of a professional. May your water heater reign supreme, providing you with endless warmth and tranquility.

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If you own a Rheem tankless water heater and are encountering error code 12, this video will guide you through the process of cleaning the burner. Learn how to troubleshoot and resolve this issue effectively.

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Step 4: Inspecting the Gas Lines

Unveiling the Mysteries of the Rheem Tankless Water Heater Code 12 Error In the realm of troubleshooting, where the enigmatic Code 12 error lurks, an exploration of the gas lines becomes an imperative quest. Behold, the path to enlightenment:

1. Traverse the realm, attuned to the signs of gas leaks – the sibilant whispers, the pungent odors, the scars upon the lines themselves. Should you encounter a leak, swift action is paramount, for the sake of your safety.

2. Seek the heart of the matter, where the gas line connections reside. There, ascertain their firmness and security, ensuring each connection is bound with steadfast precision. For loose fittings, like rebellious souls, can sow the seeds of gas leakage and awaken the dreaded Code 12 error.

3. Pierce through the veil of obstruction, for within the gas lines, hidden adversaries may dwell. Debris and detritus, formidable foes, may impede the gas flow and summon the Code 12 error. Engage in thorough inspection, banishing any blockages that dare to impede.

By embarking upon this noble quest, by scrutinizing the gas lines for leaks, fortifying the connections, and vanquishing any obstructions, you shall conquer the treacherous Code 12 error that plagues your Rheem tankless water heater. Should uncertainty or unease beset you, seek the aid of the wise and skilled professionals, for they possess the knowledge and prowess to guide you towards triumph.

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Fun Fact: Rheem tankless water heaters can provide endless hot water, saving you money on energy bills compared to traditional tank water heaters.


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Step 5: Checking the Venting

To maximize the performance of your Rheem tankless water heater, proper venting is vital. It enables the safe release of combustion gases and ensures efficient operation. Venting problems, such as blocked vents or incorrect installation, can trigger the Code 12 error and disrupt airflow, leading to heater shutdown.

Follow these steps for optimal venting: adhere to the manufacturer’s guidelines when installing the venting system, check for any obstructions in the vents, and ensure the vent size matches your heater’s capacity. By conducting regular maintenance, including annual inspections and cleanings, you can prevent venting issues and maintain the smooth operation of your Rheem tankless water heater.

1/3 Resetting Your Rheem Tankless Water Heater: A Comprehensive Guide

Achieving peak performance from your Rheem tankless water heater requires a crucial step: resetting. By regularly resetting your unit, you can resolve common issues and maintain its efficiency. Allow me to guide you through the process and provide troubleshooting tips to ensure a smooth operation.

Step 1: Power Down Before resetting, it is important to turn off the power. This can be done by switching off the breaker or unplugging the unit. Step 2: Patience is Key Give the system a few minutes to fully shut down.

This will discharge any residual power and prepare it for a fresh start. Step 3: Restart Now it’s time to turn the power back on. Once initiated, your water heater will begin its startup sequence, ready to provide you with hot water whenever you need it.

Troubleshooting Tips : To address specific problems, check the control panel for error codes. These codes can provide valuable information about the issue at hand. Additionally, it is crucial to ensure an adequate gas supply and inspect the gas line for any blockages.

Addressing plumbing connection leaks promptly is also essential for optimal performance. By following this guide and utilizing the troubleshooting tips, you can ensure the efficient operation of your Rheem tankless water heater. Regular resets will help maintain its performance and keep your hot water flowing smoothly.

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Troubleshooting Steps for Resolving Rheem Tankless Water Heater Code 12

  1. Check the flame sensor to ensure it is clean and in proper working condition.
  2. Evaluate the gas supply to ensure it is sufficient and not interrupted.
  3. Assess the gas pressure to ensure it is within the recommended range for the tankless water heater.

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Fear not, for if you find yourself faced with the enigmatic Code 12 error on your trusty Rheem tankless water heater, you are not alone. Countless individuals have encountered this perplexing dilemma and have generously shared their wisdom on how to conquer it. One invaluable suggestion is to embark on a thorough cleansing of the flame sensor, as this oftentimes serves as the key to unlocking the solution behind the Code 12 error.

Additionally, it is prudent to inspect the connections leading to the flame sensor, as any loose or damaged components may contribute to the conundrum. Should the need arise, do not hesitate to consider procuring a new flame sensor altogether. Should the issue persist despite your valiant efforts, it would be wise to seek the guidance of Rheem’s esteemed customer support.

Armed with an abundance of knowledge, their dedicated professionals will graciously assist you in navigating the treacherous waters of troubleshooting, providing you with the solutions you seek. To steer clear of future encounters with the dreaded Code 12 error, it is imperative that you bestow upon your cherished tankless water heater the gift of regular maintenance. Entrust a professional to conduct routine check-ups, allowing them to identify and address any potential issues before they metamorphose into formidable adversities.

By adhering to these invaluable tidbits of wisdom, reaching out to the esteemed Rheem customer support, and diligently maintaining the well-being of your tankless water heater, you shall forever shield yourself from the clutches of the Code 12 error and bask in the glory of optimal performance.

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Common Causes and Solutions for the Rheem Tankless Water Heater Code 12 Error

  • Flame failure is one of the most common issues that can trigger the Code 12 error on a Rheem tankless water heater.
  • The Code 12 error occurs when the heater fails to detect a flame during the ignition process.
  • The flame sensor is a crucial component that detects the presence of a flame and sends a signal to the control board.
  • If the flame sensor is dirty or covered in soot, it may not be able to accurately detect the flame, leading to a Code 12 error.
  • Ensuring a proper gas supply is essential for the tankless water heater to function correctly and avoid the Code 12 error.

2/3 Related Articles

If you’re experiencing a Code 12 error on your Rheem tankless water heater, rest assured that you’re not alone in this predicament. In this article, we aim to provide you with troubleshooting tips tailored specifically for Rheem tankless water heater models, enabling you to resolve the issue promptly. While it is often assumed that a faulty flame sensor is responsible for the Code 12 error, it’s essential to understand that there are other potential causes.

Insufficient gas supply or low gas pressure can also contribute to this error. By familiarizing yourself with these factors, you can effectively troubleshoot and rectify the Code 12 error. Furthermore, it is crucial to acknowledge the significance of professional maintenance in preventing Code 12 errors.

Regular maintenance conducted by a qualified technician can detect and address potential issues before they escalate into major problems. This comprehensive maintenance routine involves inspecting the gas valve, verifying the gas pressure regulator, and checking the gas lines for any leaks or blockages. To successfully resolve the Code 12 error, it is imperative to have access to troubleshooting tips tailored specifically to your Rheem tankless water heater model.

Additionally, being aware of common misconceptions surrounding the error and recognizing the importance of professional maintenance can help prevent future occurrences. Stay informed and don’t hesitate to reach out to Rheem customer support for further guidance and assistance.


In conclusion, understanding the Code 12 error and troubleshooting steps for Rheem tankless water heaters can greatly benefit users experiencing this issue. By following the step-by-step guide and checking the flame sensor, evaluating the gas supply, assessing gas pressure, inspecting the gas lines, and checking the venting, users can effectively troubleshoot the error. Additionally, the comprehensive guide on resetting the water heater and the preventive measures provided can help users avoid future Code 12 errors.

This article provides valuable information and solutions for users seeking assistance with their Rheem tankless water heater. For more helpful articles on similar topics, we recommend exploring our range of related articles.


What is code 12 on a tankless water heater?

If your Rinnai hot water unit is displaying error code 12, it means there has been a flame failure in the system. This error code is an indication that the unit is not detecting a flame in the burner box.

What is code 12 on Rheem tankless heater?

An error code 12 signifies that there is a flame loss in the unit. This error occurs when the unit detects a flame, but the flame becomes weak and is extinguished during operation. The error code serves as a warning to address the issue and ensure the proper functioning of the unit.

What are the codes for Rheem water heater?

If you encounter Error Code 03, it means there is a filter damage in your system. To resolve this issue, you should book a service call with Rheem Service by calling them at 13 10 31. Another potential problem is Error Code 05, which indicates that the filter has not been cleared. Additionally, Error Codes 11 and 12 signify ignition failure and flame failure respectively.

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