Tankless Water Heater Troubleshooting: Quick Fixes for Common Issues

tankless water heater troubleshooting

Last updated on April 26th, 2024 at 05:20 am

Tankless water heaters are an efficient alternative to traditional water heaters, providing hot water on demand without the need for a storage tank. The benefits of these systems include energy savings, space efficiency, and a potentially endless supply of hot water.

However, like any appliance, they can encounter problems that require troubleshooting. Understanding the workings of your tankless water heater unit can help you recognize the signs of trouble and determine the best course of action.

Before you start your tankless water heater troubleshooting journey, it’s important to familiarize yourself with common issues such as error codes, inadequate hot water supply, mineral or sediment buildup, electrical problems, gas supply issues, and temperature fluctuations.

By learning how to perform basic maintenance and resolving some of these common problems, you can ensure your tankless water heater operates effectively and efficiently. If you encounter issues beyond your expertise, seeking professional assistance is advisable to maintain the longevity and safety of your tankless water heating system.

Key Takeaways

  • Recognize common tankless water heater issues to effectively troubleshoot and maintain your system.
  • Perform regular maintenance to prevent mineral or sediment buildup and ensure efficient operation.
  • Consult a professional for complex problems like gas or electrical issues to ensure safety.

Understanding Tankless Water Heater Systems

Tankless hot water heaters, also known as on-demand or instantaneous water heaters, provide hot water only as it is needed. Tankless water heaters, in contrast to traditional storage models, heat water on demand without the need for a storage tank, resulting in greater energy efficiency.

Here’s what you should know about how these systems work:

  • Heat Exchanger: Upon activating a hot water faucet, cold water flows through your plumbing system and into the tankless unit. Inside, a heat exchanger raises the water temperature to match your predetermined setting.
  • Energy Source: Tankless water heaters can run on various energy sources, including electricity, natural gas, or propane. The energy source affects the installation process and operating costs.


  • Space-saving: Their compact size frees up space in your home.
  • Energy-efficient: You only heat the water you use, which could mean lower utility bills.
  • Continuous supply: You get an endless stream of hot water, making them ideal for families.


  • Flow Rate: The amount of hot water generated is measured in gallons per minute (GPM). Ensure the model you choose meets your peak hot water demands.
  • Initial Cost: They tend to be more expensive upfront compared to traditional models.
  • Maintenance: Regular maintenance is crucial to ensure a long lifespan and prevent issues.

By understanding these basics of tankless water heater systems, you’ll be better equipped to decide if this solution is right for your home and to troubleshoot any problems that may arise.

Common Error Codes and What They Mean

When your tankless water heater displays an error code, it’s giving you a critical clue to the underlying issue. Understanding these codes can help you quickly identify and address the problem.

Ignition Failure

If you’re seeing an error code pointing to an ignition failure, it’s possible that your water heater is unable to light the burner. Check to ensure that your gas supply is on and that the water heater is properly connected to the power source.

Flame Failure

A flame failure error code typically means that the heater’s burner lit, but it went out unexpectedly. Make sure that there is no problem with your gas pressure, and confirm that the venting isn’t obstructed, which could be extinguishing the flame.

Exhaust Blockage

An error code indicating an exhaust blockage suggests that the venting system is impeded. It’s important to ensure that the vent pipes are clear of obstructions to maintain adequate flue gas venting.

Maintenance Tips for Tankless Water Heaters

Regular maintenance is crucial to ensuring your tankless water heater operates efficiently and has a long lifespan. Here’s what you should do:

Flush the System

At least once a year, flush out the unit to remove any mineral buildup. This is especially important in areas with hard water. You can use a vinegar solution for this task. Remember to restore the power and water supply after doing so.

Inspect for Leaks

Check the surrounding area for signs of leaks regularly. Catching a leak early can prevent further damage to the system.

Clean the Air and Water Filters

Your unit has filters that need to be cleaned periodically:

  • Air filter: Usually a mesh screen that requires routine cleaning to ensure proper airflow.
  • Water filter: Needs to be rinsed to prevent blockage and maintain water pressure.

Monitor the Pressure Relief Valve

Ensure the pressure relief valve is functioning correctly to avoid excessive pressure within the unit that could cause damage.

Check the Venting System

Proper venting prevents backdrafts and ensures efficient operation. Clear any obstructions and verify that the venting is in good condition.

Keep a Maintenance Log Record the dates of:

  • Flushing
  • Filter cleaning
  • Inspections

This helps you stay on top of maintenance and can be useful for any warranties or services. For more details on servicing and troubleshooting tankless water heaters, consider the insights provided by the guide Audel HVAC Fundamentals.

Troubleshooting Inadequate Hot Water Supply

When you notice your tankless water heater isn’t providing enough hot water, a few factors might be at play. It’s crucial to address these issues promptly to ensure you have a consistent supply of hot water when needed.

Similar to most tankless water heaters, if your unit lacks a buffer tank or recirculation pump, it might require a minute or two to heat the water before it reaches the tap. Additionally, the distance between the water heater and the fixture influences the speed at which hot water is delivered.

Flow Rate Adjustment: Check your water heater’s flow rate. If it’s set too high, your heater may struggle to heat the water adequately. Consider reducing the flow rate to increase the water’s temperature.

Examine the Temperature Setting:

  • Ensure the temperature setting is not too low; it should be suitable for your needs.
  • Adjust the temperature upwards in small increments to see if there’s an improvement.

Check for Crossed Connections:

  • Crossed hot and cold water connections can lead to mixed water temperatures.
  • You can test for this by shutting off the water supply and checking if hot water is still flowing, which would indicate a crossing.

Descale Your Water Heater:

  • Scaling from hard water can reduce the effectiveness of your heater.
  • Perform a descaling process by following your manufacturer’s instructions.

Inspect for Malfunctioning Parts:

  • Elements like the gas burner or ignition may be failing. A professional may need to assess these components.
  • Check for error codes on the display and refer to your manual for specific troubleshooting steps.

Examine the Demand:

  • Ensure multiple appliances aren’t running simultaneously, which can overwhelm your heater.
  • Stagger the use of appliances to balance the hot water demand.

Professional Inspection: If the above steps don’t resolve the issue, it might be time to contact a professional for a thorough inspection and potential repairs.

Dealing With Mineral Buildup and Hard Water

When using tankless water heaters in areas with hard water, mineral buildup can affect performance and efficiency. It’s essential to tackle this head-on to maintain your unit’s longevity and functionality.

Descaling Process

Step 1: Shut off the power to your tankless water heater. Step 2: Close the main water valves and remove the purge port valve caps. Step 3: Attach hoses to the service valves and pour a specially formulated descaling solution or white vinegar into the unit. Step 4: Open the service valves and circulate the solution with a submersible pump, following the manufacturer’s recommended time. Step 5: Flush the unit with fresh water, reattach the valve caps, and turn the power back on.

Preventive Measures

  • Install a water softener to reduce mineral content before it enters your heater.
  • Perform regular maintenance flushes to prevent severe scale accumulation.
  • Use in-line filters to catch debris and sediment which can contribute to scaling.
  • If the output temperature sensor is broken, replace it.
  • Check the anode rod annually, replacing it if necessary, to protect against corrosion.

Electrical Issues and How to Address Them

If your electric tankless water heater is experiencing electrical problems, it’s crucial to handle them with care. Here are some common issues and how to address them:

  • No Power: First, check your circuit breaker or fuse box. If the circuit has tripped or a fuse has blown, reset the breaker or replace the fuse. If this happens frequently, contact an electrician as there could be a larger issue at play.
  • Tripping Breaker: If your water heater frequently trips the circuit breaker, it could be a sign of an electrical overload. Make sure your system is on its own dedicated circuit. If the problem persists, it might indicate a short circuit within the heater. It’s best to call a professional.
  • Faulty Wiring: Over time, wiring can degrade or become loose. If you’re comfortable, turn off the power and inspect the wiring connections to the heater. Tighten any loose connections, but if wires appear damaged or burnt, it’s important to call in an electrician.

Here’s a quick checklist:

No PowerCircuit breaker/Fuse BoxReset breaker or replace fuse
Tripping BreakerElectrical OverloadProfessional inspection / Repair
Faulty WiringWiring ConnectionsTighten or call an electrician

Remember to always prioritize safety when dealing with electricity. If you’re ever unsure or uncomfortable, it’s wise to seek professional help. Your safety is paramount when addressing these electrical issues.

Gas Supply Problems and Solutions

When you’re facing issues with your tankless water heater, one common area to inspect is the gas supply. Ensuring a consistent and adequate gas supply is crucial for the proper functioning of your heater. Here’s how you can troubleshoot gas supply problems:

Insufficient Gas Flow


  • Water temperature fluctuates
  • Heater shuts off during use


  • Check your gas meter to make sure you have service.
  • Inspect the gas lines for any bends or damage that could restrict flow.’
  • Check that the gas valve is fully opened.

Gas Leak


  • Smell of gas near the heater
  • Hissing sound from gas lines


  • Do not try to repair it yourself. Exit your home immediately.
  • Contact your gas company or a professional technician.

Dirty Burner


  • Yellow flame instead of blue
  • Soot buildup


  • Before attempting any cleaning, ensure the gas supply is turned off.
  • Gently clean the burner with a soft brush or compressed air.

Incorrect Gas Pressure


  • Heater won’t ignite
  • Error code displayed


  • Utilize a gas pressure gauge to check pressure.
  • Adjust the gas regulator as necessary, following the manufacturer’s specifications.

Always prioritize safety when handling gas-related issues, and consider professional help for complex problems to ensure everything is addressed correctly and safely.

Temperature Fluctuations and Fixes

If you’re experiencing temperature fluctuations or cold water sandwich effect with your tankless water heater, you’re not alone. This occurs when you encounter a sudden surge of cold water amidst your warm water shower experience. Here’s how you can identify and fix some of the most common issues.

Check the Flow Rate

  • Ensure the water flow rate is above the minimum activation rate.
  • Flow sensors may need cleaning or replacing if the flow rate seems adequate.

Clean the Inlet Filter

  • Your heater’s inlet filter may be clogged.
  • Clean the filter to improve water flow and temperature consistency.

Examine the Gas Pressure

  • If you have a gas tankless water heater, check the gas pressure.
  • Inadequate gas pressure can lead to uneven heating.

Inspect for Cross-Connections

  • Shut off the cold water inlet valve.
  • Make sure there are no cross-connections within your plumbing system.
  • Accidental mixing of cold and hot water can cause fluctuations.

Calibrate the Thermostat

  • Recalibrate the thermostat according to the manufacturer’s instructions.
  • If calibration doesn’t work, the thermostat may need to be replaced.

Look at the Heat Exchanger

  • Scale build-up in the exchanger can impede heat transfer.
  • Regularly descaling the heat exchanger can prevent and fix this issue.

If these steps don’t resolve the temperature fluctuations, you might need professional help. A certified technician can troubleshoot deeper issues that may be beyond the scope of DIY fixes. Remember to always prioritize safety when performing any maintenance on your tankless water heater.


When tackling tankless water heater problems, remember that routine maintenance can prevent most problems. If you’re experiencing a lack of hot water or other common issues:

  • Check error codes and consult your user manual.
  • Regularly descale your heater to combat hard water buildup.
  • Ensure gas and electric supplies are consistent and sufficient.
  • For ignition failures, assess your ventilation and gas pressure.
  • Remember, diy repairs carry risks, and professional help is sometimes needed.
  • Regular annual maintenance is critical.

With proper care, your tankless water heater can be an efficient, long-lasting solution for your hot water needs. Stay informed, stay safe, and don’t be afraid to call a pro when in doubt.

Frequently Asked Questions

Troubleshooting your tankless water heater can sometimes be as simple as performing a reset or ensuring proper maintenance. Below are common questions and straightforward solutions to help you get your hot water flowing again.

How do I reset my tankless water heater?

To reset your tankless water heater, locate the reset button, typically found on the unit’s front panel. Press and hold this button for a few seconds. If your unit has a remote control, a reset may also be performed through its interface.

What should I do when there is no hot water to the kitchen sink from my tankless unit?

Ensure the unit is powered and the circuit breaker hasn’t tripped. If power isn’t the issue, check to see if any error codes are displayed and refer to your manual for specific remedies. If there are no error codes, the problem might be isolated to the sink—check the hot water valve underneath to make sure it’s fully open.

What are some troubleshooting tips for a Rinnai tankless water heater experiencing common problems?

For a Rinnai tankless water heater, first check for any error codes, which can guide you to the issue. It might be a simple fix like cleaning the inlet filter or ensuring proper venting. Regular maintenance like flushing the system to prevent scale build-up can also prevent many common issues.

What are some troubleshooting tips for a Rheem tankless water heater experiencing common problems?

If you’re dealing with a Rheem tankless water heater, ensure it’s receiving enough gas pressure, and that the vents are not obstructed. If you find an error code, refer to your user’s manual for specific troubleshooting steps. Sometimes, resetting the unit or cleaning the water and air filters can resolve the issue.


  • Edmund Yeo

    🌱 I'm passionate about sustainable living and renewable energy, and I'm thrilled to share my journey towards a greener, brighter future with you. Join me as I explore the latest innovations, eco-friendly lifestyle tips, and inspiring stories from the forefront of the green energy revolution. Note: This website uses affiliate links which may earn a commission for purchases made at no additional cost to you.

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