Rheem Tankless Water Heater Not Heating No Error Code: Expert Solutions

Rheem tankless water heaters are renowned for their efficiency and reliability, providing endless hot water on demand. However, like any sophisticated appliance, they can encounter issues, one of the most perplexing being when the unit stops heating water without displaying any error codes. This situation can leave homeowners in a bind, unsure of where to start troubleshooting.

Understanding the nuances of tankless water heater operations is key to diagnosing and resolving such issues. Despite their advanced technology, these systems can falter due to a variety of reasons, from gas supply problems to electrical connection issues. Knowing how to identify these causes is the first step towards a solution.

This guide aims to shed light on the common reasons behind a Rheem tankless water heater not heating and how to troubleshoot these problems effectively. With a focus on practical steps and preventive measures, we endeavor to help you restore your hot water supply and ensure your system operates at peak efficiency.

Common Reasons for Rheem Tankless Water Heater Heating Issues

When a Rheem tankless water heater fails to provide hot water, and no error codes are displayed, it can be puzzling and frustrating. Several common issues might be at play, affecting the heater’s ability to function correctly. Identifying these issues is the first step toward troubleshooting and resolving the problem.

Gas Supply Problems

Gas-powered tankless water heaters require a steady and sufficient supply of gas to heat water effectively. Issues with the gas supply can lead to inadequate heating or complete failure to heat:

  • Gas Line Size: An undersized gas line restricts the flow of gas to the heater, preventing it from operating at full capacity.
  • Gas Pressure: Incorrect gas pressure, whether too low or too high, can impede the heater’s efficiency. Low pressure doesn’t provide enough fuel for the burner, while high pressure can be dangerous and lead to system shutdown.
  • Gas Valve: A partially closed gas valve limits the amount of gas reaching the unit. Ensure the valve is fully open for optimal operation.
  • Air in the Gas Line: Air pockets in the gas line can disrupt the steady flow of gas to the burner, affecting performance.

Water Flow Issues

Tankless water heaters are designed to activate and heat water as it flows through the unit. Problems with water flow can thus directly impact heating:

  • Minimum Flow Rate Not Met: If the water flow is below the heater’s minimum activation threshold, the unit may not turn on. This can happen with low-flow faucets or fixtures.
  • Debris and Scale Build-up: Over time, sediment, debris, or scale can accumulate in the water lines or the heater’s internal components, restricting water flow and affecting heat exchange efficiency.
  • Water Line Obstructions: Bends, kinks in flexible water lines, or partially closed valves can reduce the water flow to the heater, preventing proper operation.

Electrical Connections

For electric tankless water heaters, and even for gas models with electric components, electrical issues can prevent the heater from functioning:

  • Power Supply: An inconsistent or inadequate power supply can cause the unit to malfunction. Ensure the heater is connected to a reliable power source.
  • Tripped Circuit Breaker or Blown Fuse: Electrical faults, surges, or overloads can trip a circuit breaker or blow a fuse, cutting power to the heater.
  • Faulty Ignition System: In gas models, a faulty ignition system due to electrical issues can prevent the burner from lighting, leading to no hot water.

System Overload

Tankless water heaters are rated for a certain capacity. If demand exceeds this capacity—such as multiple showers and appliances running simultaneously—the unit may fail to heat water adequately.

Incorrect Installation

Improper installation, including incorrect gas line size, venting issues, or electrical connections, can lead to chronic heating problems. The installation must adhere to the manufacturer’s specifications and local building codes.

Common Rheem Error Codes

  • Error Code 11: Indicates no ignition or the unit failed to detect a flame. Common causes include gas supply issues, faulty igniters, or blocked venting.
  • Error Code 29: Signifies a low water flow problem, which could be due to clogged water filters or issues within the plumbing affecting water pressure.
  • Error Code 13: Points to a problem with the air supply or exhaust. This could be from blockages in the venting or issues with the fan.
  • Error Code 76: Indicates a communication fault between the remote control and the unit’s main control board, often due to wiring issues.

These are just a few examples, and your unit might display other codes depending on the specific issue. Refer to your Rheem manual for a comprehensive list of error codes and their meanings.

Why No Error Code Might Appear

There are instances where your Rheem tankless water heater might experience issues like inadequate gas supply or restricted water flow without triggering an error code. This is because some problems, particularly those external to the unit (such as supply issues or general maintenance needs), do not fall within the parameters the error code system monitors. In such cases, thorough troubleshooting based on the unit’s performance and external inspections are necessary to identify and resolve the issue.

7 Troubleshooting Steps Tankless Water Heater Not Heating

1. Checking Gas Supply and Pressure

For Gas Models:

  • Ensure Gas Supply: Check that the gas valve is fully open to allow gas to flow to the heater. A partially closed valve can restrict the supply.
  • Inspect for Leaks: Use a gas leak detector solution or soapy water to check connections for leaks. Bubbles forming indicate a leak that needs fixing.
  • Verify Gas Pressure: Gas pressure must meet the manufacturer’s specifications for optimal performance. This usually requires a professional to measure and adjust if necessary.

2. Inspecting Water Flow

  • Check Flow Rate: Ensure the water flow rate meets or exceeds the minimum required by the heater to activate the heating process. Low-flow faucets might not trigger heating.
  • Clean Inlet Screen Filter: Locate and clean the inlet screen filter of any debris or sediment that might be restricting water flow.
  • Inspect Water Lines: Make sure there are no bends, kinks, or obstructions in the water lines that could reduce flow. Ensure all valves are fully open.

3. Verifying Electrical Connections

For Electric Models and Gas Models with Electric Components:

  • Check Power Supply: Ensure the heater is connected to a working power supply. For electric models, verify that the voltage matches the unit’s requirements.
  • Reset Circuit Breaker/Fuse: If the circuit breaker has tripped or a fuse has blown, reset the breaker or replace the fuse. If this happens frequently, consult an electrician.
  • Inspect Wiring: Look for any loose, damaged, or corroded wiring connections. Secure any loose connections and replace damaged wires, adhering to electrical safety standards.

4. Evaluating System Performance

  • Monitor Water Temperature: If the water heats but not sufficiently, adjust the temperature settings according to the manufacturer’s instructions. Be mindful of setting the temperature too high, which can increase the risk of scalding.
  • Demand Overload: If the issue occurs only when multiple taps or appliances are in use, you may be exceeding the unit’s capacity. Stagger the use of hot water to avoid overloading the system.

5. Advanced Checks

  • Examine Venting System (Gas Models): Ensure the venting system is correctly installed and free from obstructions. Improper venting can affect combustion and heater performance.
  • Check Ignition System (Gas Models): If the unit fails to ignite, it may be due to a faulty ignition system, requiring inspection by a qualified technician.
  • Descale Heat Exchanger: In areas with hard water, scale buildup can affect heating efficiency. Follow the manufacturer’s instructions to describe the heat exchanger.

6. System Reset

  • Perform a System Reset: Sometimes, simply resetting the heater can clear any glitches. Turn off the power, wait a few minutes, and then turn it back on. For some models, a specific reset procedure might be required as outlined in the user manual.

7. Consult the User Manual

  • Reference Error Codes and Troubleshooting: Even if no error code is displayed, consulting the manual for troubleshooting tips can be helpful. The manual may offer model-specific advice not covered in general troubleshooting guides.

8 Rheem Tankless Water Heater Maintenance Tips

1. Regular Cleaning and Flushing

  • Descaling: If you have hard water, scale buildup can occur in the heat exchanger, reducing efficiency and potentially causing damage. Describe your tankless water heater at least once a year by circulating a descaling solution through the unit. The frequency may increase with harder water.
  • Flush the System: Even if you don’t have hard water, it’s a good practice to flush the system annually with clean water to remove sediment and debris.

2. Filter Maintenance

  • Clean the Inlet Screen Filter: Your Rheem tankless water heater has an inlet screen filter to trap debris. Clean this filter every 6 months, or more frequently if you notice a decrease in water flow. Simply remove the filter, rinse it with water, and replace it.
  • Air Intake and Exhaust: Ensure the air intake and exhaust are clear of debris, dust, or obstructions. A blockage can affect combustion and efficiency, especially in gas models.

3. Annual Inspections

  • Professional Inspection: Have a certified technician inspect your tankless water heater annually. They can check for gas leaks, ensure proper venting, and verify that all electrical connections are secure. This is also a good time to have the system described if you haven’t done it yourself.
  • Visual Inspection: Regularly inspect your unit for signs of wear, leaks, or corrosion. Addressing these issues early can prevent more significant problems down the line.

4. Ventilation

  • Check Ventilation System: For gas models, ensure the venting system is not obstructed and is properly installed. Incorrect venting can lead to inefficient operation and safety hazards.

5. Water Pressure Regulation

  • Monitor Water Pressure: High water pressure can damage your tankless water heater over time. Install a pressure-reducing valve if your water pressure exceeds the manufacturer’s recommended levels.

6. System Settings

  • Temperature Settings: Avoid setting the temperature too high, as this can cause scaling to occur more rapidly and increase the risk of burns. A setting between 120°F and 130°F is often recommended for both safety and efficiency.

7. Seasonal Considerations

  • Winterization: If you live in a region where temperatures drop below freezing, follow the manufacturer’s instructions for winterizing your tankless water heater to prevent freeze damage.

8. Keep Documentation

  • Maintain Records: Keep a record of all maintenance activities, including descaling, filter cleaning, and professional inspections. This documentation can be valuable for warranty claims or future troubleshooting.

When to Call a Professional

Dealing with a Rheem tankless water heater that isn’t heating properly can be challenging, especially when the typical troubleshooting steps don’t lead to a solution. In some situations, it’s best to recognize when to call in a professional. Here’s how to identify those moments and understand the importance of professional intervention.

Identifying Complex Issues

Complex issues go beyond basic troubleshooting steps such as checking power supplies, gas supply, and simple resets. These can include problems with internal components, such as the control board, heat exchanger, or intricate gas and water flow mechanisms. Here are some signs that indicate the need for a professional:

  • Persistent Error Codes: If your water heater is displaying error codes that do not resolve with the recommended actions, it’s a sign of deeper issues.
  • No Hot Water Despite Troubleshooting: After going through basic troubleshooting steps, if your unit still fails to produce hot water, the cause may be complex.
  • System Instability: Frequent resets, fluctuating water temperatures, or inconsistent operation can indicate underlying problems that require expert analysis.
  • Unfamiliar Sounds: Unusual noises such as banging, whistling, or constant clicking from the unit can signal serious issues.

Safety Considerations

Tankless water heaters are sophisticated systems that combine gas, electricity, and water. Mishandling these elements can pose significant safety risks. Here’s why professional help is crucial:

  • Gas Leaks: If you suspect a gas leak (indicated by a rotten egg smell or the sound of gas escaping), do not attempt to fix it yourself. Gas leaks are dangerous and require immediate attention from a professional.
  • Electrical Hazards: Working with electrical components carries the risk of shock, especially in an environment where water is present. Professionals are equipped with the necessary tools and safety gear to handle these risks.
  • Carbon Monoxide: Incorrect venting or combustion issues can lead to carbon monoxide buildup, a dangerous and odorless gas. Professionals can ensure that your system is vented correctly.
  • Water Damage: Improper handling of water connections can lead to leaks, potentially causing water damage to your property. A professional can ensure all connections are secure and leak-free.

FAQs About Rheem Tankless Water Heaters

Why is my Rheem tankless water heater not producing hot water?

There could be several reasons, including issues with the gas supply, electrical connections, water flow, or system settings. Begin with basic troubleshooting steps such as checking for power, ensuring the gas supply is on and adequate, verifying water flow, and checking the system settings. If these steps do not resolve the issue, it may be necessary to delve into more advanced troubleshooting or call a professional.

What do I do if I see an error code on my Rheem tankless water heater?

Refer to your user manual for a detailed explanation of the error code. Some codes may suggest simple fixes like resetting the unit or checking for obstructions in the venting system, while others may indicate more serious issues that require professional service.

How often should I describe my Rheem tankless water heater?

It is recommended to descale your tankless water heater at least once a year, especially if you have hard water. In areas with very hard water, more frequent descaling may be necessary to prevent buildup and maintain efficiency.

Can I install a Rheem tankless water heater myself?

While individuals with good DIY skills can install a tankless water heater, it’s strongly recommended to have it installed by a certified professional. This ensures proper installation according to local codes and safety standards, and it may also be required to maintain the warranty.

Why doesn’t my Rheem tankless water heater have an error code, even though it’s not working properly?

Not all issues trigger an error code. Problems like inadequate gas pressure, insufficient water flow, or certain electrical issues might not generate a code. Begin with basic troubleshooting, and if the issue persists, consult a professional.

How can I improve the efficiency of my Rheem tankless water heater?

Regular maintenance, including descaling, checking filters, and ensuring venting systems are clear, can greatly improve efficiency. Additionally, setting the temperature to a reasonable level (around 120°F) can also help reduce energy consumption.

Is it worth upgrading to a newer model of Rheem tankless water heater?

If your current unit is old, frequently requires repairs, or lacks features that meet your needs, upgrading to a newer model can be beneficial. Newer models tend to be more energy-efficient, have advanced features, and may offer better performance and reliability.

How long do Rheem tankless water heaters last?

With proper maintenance, a Rheem tankless water heater can last up to 20 years or more. Regular descaling, cleaning, and annual inspections can extend the lifespan of your unit.


Facing a Rheem tankless water heater that isn’t heating up without any error codes can be a daunting issue for any homeowner. This guide has walked you through the possible causes, from gas supply and water flow issues to electrical connections and system overloads, providing a comprehensive overview of the steps to troubleshoot and rectify these problems. It emphasized the importance of regular maintenance, including descaling and inspecting your unit, to ensure optimal performance and longevity of your Rheem tankless water heater.

When troubleshooting doesn’t resolve the issue, or if you encounter complex problems that go beyond basic fixes, calling in a professional becomes imperative. Professional technicians can provide the expertise needed to safely and effectively address issues related to gas leaks, electrical hazards, and system complexities that are not advisable for DIY solutions. They ensure that your water heating system complies with safety standards and operates efficiently, safeguarding your home and family.

In summary, while Rheem tankless water heaters are designed for efficiency and reliability, encountering heating problems can be a complex challenge. This guide serves as a starting point for troubleshooting, but it also underscores the significance of professional intervention for complex issues. By following the recommended maintenance tips and seeking professional help when needed, you can enjoy the benefits of your tankless water heater for years to come. Remember, the key to resolving heating issues lies in understanding the problem, taking appropriate corrective actions, and recognizing when to seek expert assistance.

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