How to Fix Rheem Tankless Water Heater Code 12

By SmartHomeBit Staff •  Updated: 06/08/23 •  17 min read

Understanding Rheem Tankless Water Heater Code 12

Rheem Tankless Water Heater Code 12 is more than just a simple error code. It’s an indicator of a potential issue that could lead to serious problems in your water heating system. In this section, we’ll explore what exactly the Code 12 means and what could be causing it. We will also discuss how Code 12 serves as an early warning system and helps in identifying any problems with your Rheem Tankless Water Heater.

What is Rheem Tankless Water Heater Code 12?

Code 12 errors on Rheem Tankless Water Heaters can be a hassle. It usually means the ignition or heat exchange and exhaust venting system is having issues. Poor installation, lack of maintenance, or low gas pressure may be to blame.

The flame sensor or ignitor coil could be malfunctioning. Or, limited airflow or low gas pressure might be the cause. This requires technical assistance for troubleshooting.

You can try cleaning the flame sensor or improving airflow quality. Clogs, replacing ignitor coils or control valves might help too.

It’s important to address Code 12 quickly. Ignoring it can lead to more maintenance difficulties, reducing safety and efficiency, while increasing energy expenses. Hot showers lovers, take note!

How does Rheem Tankless Water Heater Code 12 indicate water heater problems?

The Rheem Tankless Water Heater Code 12 is an error code that is displayed on the unit’s digital display panel. It indicates an issue with the tankless water heater and is a warning that needs to be addressed immediately.

Low gas supply pressure is a common cause of the Code 12 error. The heating system of the Rheem tankless water heater needs gas to work properly. If the flow to the unit is blocked, the components can overheat and lead to other issues.

Other possible causes of Code 12 errors include low water pressure, clogged filter, faulty thermostat, dirty flame sensor, filthy flame rod, and clogged venting pipes. If any of these issues occur, it is essential to get help quickly to avoid more serious damage.

In conclusion, the Rheem Tankless Water Heater Code 12 alert is important. It shows no or low gas supply pressure issues, which require immediate attention.

Common Causes of Rheem Tankless Water Heater Code 12

Dealing with a Rheem tankless water heater code 12 can be frustrating. In this section, we will explore some common causes of this error code and how they can be addressed. From low water pressure to a clogged filter, we will cover various sub-sections and provide insights that will help you better understand the issue and how to tackle it.

Low water pressure

Encountering low water pressure when operating a Rheem tankless water heater can cause issues. You’ll get an error code 12, which means the water flow isn’t enough for the system to work.

This is a common problem in homes. It could be due to high drops in pipes, air bubbles, clogged filters or a broken valve. These could damage electric appliances like thermostats, ignitor coils and gas control valves.

Low water pressure needs sorting out quickly as it can harm your health and building standards. Too little water can make parts too hot and create scale on metal surfaces, causing corrosion.

Pro Tip: To keep your tankless water heater working well and stop Code 12 errors due to low water pressure, check your plumbing regularly. Clean filters and other parts to get the best performance.

Let’s hope you don’t need a filter to find love – and a hot shower!

Clogged filter

Rheem Tankless Water Heater Code 12 means there’s a combustion issue. It’s often caused by a clogged filter. This stops water flow and heat exchange. Clogs in air and water filters reduce pressure and hot water supply. Dirty filters can’t regulate temperature or keep up with demand. This can lead to Code 11 or 29 too. Cleaning the filters helps, but regular monitoring and maintenance is better. That’ll help stop the clogged filter issue and keep the water heater running optimally.

Faulty thermostat

When the Rheem tankless water heater shows Code 12, it’s a sign of a problem. A faulty thermostat could be the cause. It’s responsible for controlling and regulating the temperature. If it’s not working right, the water won’t heat up properly. This leads to Code 12.

Plus, a bad thermostat can bring other issues. These issues include leaks and incorrect temperature readings.

It’s important to take care of the issue quickly. Faulty thermostats can reduce energy-efficiency and raise energy costs.

Pro Tip: If you’re not sure how to troubleshoot or fix the thermostat, get help from a professional technician. They have the right tools and knowledge to diagnose and repair any issues.

Insufficient gas flow

If you get a Rheem Tankless Water Heater Code 12, it may mean there’s insufficient gas flow. This happens when not enough gas is reaching the unit.

There can be many causes. For example, gas lines may be too small. Or, there might be clogs in the venting system. Or, the regulator could be faulty.

In some cases, insufficient gas flow could mean other issues with the water heater. For instance, dirty flame sensors or faulty thermostats can affect temperature readings. This can lead to less-than-optimal gas flow. So, it’s important to fix these components first, before attempting fixes for gas flow issues.

Dirty flame sensor

A dirty flame sensor is a common cause of Rheem Tankless Water Heater Code 12. This is because impurities like soot and dust can prevent it from detecting the flame correctly, resulting in an error code 12. This code means that the heater sees the flame as either absent or weak, then shutting off the gas flow instantly.

Low gas pressure can also lead to the same issue. Cleaning may not always solve this problem. It may need technical help.

To prevent problems arising, it’s important to clean and maintain your Rheem Tankless Water Heater regularly. Doing regular checks can help spot and fix small troubles before they become major. The flame sensor is a vital component of the heater, so make sure to keep it clean and maintained.

Filthy flame rod

The Rheem tankless water heater system relies on the flame rod – a vital component. Over time, it may develop carbon buildup – a common problem known as “Filthy Flame Rod” to technicians and plumbers.

Grime, soot, and other carbon deposits can stop the flame rod from detecting heat. This leads to a system shutdown and code 12 error. It can also cause cold water supply or flooding.

Regular maintenance is key to prevent this problem. If you get a code 12 error, you must address it quickly. Professional help or DIY steps are needed. Ignoring it can stop your heater from working until fixed.

Don’t let your heater have all the fun! Keep your Rheem tankless in top shape. Address filthy flame rod issues and do regular maintenance.

Clogged venting

When Code 12 is displayed on a Rheem tankless water heater, it’s an indication of a venting system issue. This could be due to a blocked vent. The venting system expels combustion byproducts from the home. Blocked vents cause these byproducts to stay inside the house, and can be harmful to those living in it.

Rheem tankless water heaters need proper ventilation to work efficiently. A clogged venting system reduces the appliance’s performance, resulting in higher energy bills. To fix this issue, professionals must clean not only the vent, but also the burners and heat exchangers. All connections must be properly sealed too, for safety.

If your Rheem tankless water heater has a bad regulator, it’s important to get it fixed. A bad regulator decreases gas flow, and affects the appliance’s performance. It’s essential to get a professional to inspect and repair the regulator, in order to make sure the Rheem tankless water heater works optimally.

Bad regulator

The Rheem tankless water heater code 12 could mean a bad regulator. This part of the gas supply system can cause many difficulties, such as inconsistent heat, limited hot water, incorrect temperature settings, or even unsafe conditions.

To avoid problems, the faulty regulator must be changed. Only original parts should be used, otherwise, more big issues may come up in the future.

A friend of mine had lukewarm water, even when setting it to the highest temperature. It wasn’t until a technician found the bad regulator part that it was fixed. It is now working well and they get hot showers again.

So, it’s important to address and fix any issues with the regulator in your Rheem tankless water heater quickly. This keeps it running optimally and safely.

Too small gas lines

If your Rheem Tankless Water Heater displays Code 12, it could mean the gas line is too small. This restricts gas flow, reducing efficiency and heating power. It may show an error to signal there’s not enough gas pressure.

Having small pipes may not always trigger an error message. But, it’s important to check they are large enough for efficient operation. Upgrading to larger pipes may be necessary.

Also, ensure system components are compatible and efficient. Ignoring Code 12 could mean freezing in the shower!

It’s essential to address this issue quickly. This prevents compromising performance and safety.

Importance of Addressing and Fixing Code 12

If your Rheem tankless water heater display shows code 12, it is important to take action right away. This code indicates an issue with the flame sensor, which could lead to hazardous conditions if not addressed.

The possible causes of code 12 are a dirty or faulty sensor, gas pressure issues, or venting blockage. Ignoring it could cause health issues such as carbon monoxide poisoning or an explosion.

To fix this, switch off the water heater and inspect the sensor. If the sensor looks clean and undamaged, a licensed plumber should be contacted to diagnose and repair the issue.

Regular maintenance checks for your tankless water heater will help prevent code 12 from happening. Cleaning the sensor and proper venting can prevent dangerous situations.

Rheem recommends having a licensed plumber install and maintain your tankless water heater to avoid code 12 and improve efficiency. Regular maintenance and repair will ensure the tankless water heater works safely and effectively to provide hot water.

In summary, code 12 on your Rheem tankless water heater must be addressed immediately to avoid potential safety hazards. Regular maintenance and the use of licensed professionals for installation and repair is essential.

Fixing Rheem Tankless Water Heater Code 12

If you own a Rheem Tankless Water Heater, you might have encountered the error code 12, which indicates a flame failure. Don’t worry, as we’ve got you covered with some practical solutions. In this section, we’ll share multiple sub-sections to help fix the Rheem Tankless Water Heater Code 12 issue. From improving airflow to checking your heater’s power supply, we’ll explore the various ways you can troubleshoot the code 12 error on your Rheem Tankless Water Heater.

Cleaning the dirty flame sensor

Issues with your Rheem tankless water heater? Seeing code 12? Time to clean the dirty flame sensor! It’s easy – just a 3-step process.

  1. First, switch off the power and water to the unit.
  2. Next, locate the sensor near the burner.
  3. Finally, scrub it with a firm-bristled brush.

Remember to reattach all wires and hoses after cleaning, as well as restore the electrical and water connections.

Be careful of the wires – they may still have electric charges when switched off. Keeping the air filters around the heater area clean can help keep the flame sensor clean and avoid future problems.

Regular cleaning maintenance can prevent many of the issues associated with code 12 on Rheem tankless water heaters. So, you might need a new ignitor coil or a fresh start with your water heater!

Replacing a bad ignitor coil

Fixing code 12 on a Rheem tankless water heater may involve replacing a bad ignitor coil. It is important to be careful when handling gas appliances.

  1. Step one: turn off the gas, water, and electricity to the unit.
  2. Remove the cover to access the ignitor coil.
  3. Disconnect the wire harness from the old coil and take it out of its bracket.
  4. Put the new coil in place and attach the wire harness.
  5. Put the cover back on and turn back on the gas, water, and power.
  6. Test if code 12 has been fixed.

Replacing an ignitor coil must only be done by an expert technician. Doing it without proper training can lead to injury or property damage. Make sure the new coil is an exact match for the Rheem model. Mismatched parts could cause more issues.

DIY repairs on tankless water heaters can void the warranty. Professional help can keep you safe and protect the warranty. A Consumer Reports study shows that people can save up to 5% on energy bills yearly by maintaining tankless water heaters.

Therefore, replacing a bad ignitor coil is key for fixing code 12 on a Rheem tankless water heater. It is wise to get professional help and follow proper steps to stay safe and keep the warranty.

Checking gas and power supply

Gas and electricity are key for a Rheem Tankless Water Heater to work well. If these are not working, Code 12 can happen. To avoid this, check the gas and power. Start with the gas valve, make sure it’s on. Then, look at the gas line and regulator. Check the circuit breaker too. And see if the power outlet is good. Use a multimeter to test the voltage. Do this before anything else! If there’s still an issue, call a professional.

For instance, a customer with a two-year-old Rheem water heater had Code 12. The gas line was too small. After they upgraded the line size as recommended, hot water was back.

Therefore, check the gas and power supply of a Rheem Tankless Water Heater. This will help it to run smoothly.

Improving airflow

To keep Rheem tankless water heaters running smoothly, it’s important to improve the airflow. A blockage in the venting system can lead to incomplete combustion and an error code 12. Follow these 6 steps to improve the airflow:

  1. Check for obstructions in the venting system. Birds’ nests or debris can cause a blockage.
  2. Clean the intake filter twice a year. Dirt buildup can clog it.
  3. Consult a technician to ensure proper venting design. Improper design limits air supply.
  4. Leave a minimum clearance space of about a meter around the heater. Don’t place items near it.
  5. Install louvers on interior doors or install exterior vents.
  6. Schedule periodic inspections by a technician to prevent blockages.

Regular maintenance cleanings are key. Plus, repairs like fixing a faulty thermostat, checking gas and power supply, and replacing bad gas control valves can also help. Replace a bad gas control valve and your hot water will be back in no time!

Replacing a bad gas control valve

When your Rheem tankless water heater displays Code 12, it’s an ignition failure. This could be due to a faulty gas control valve. To replace it, here are 5 steps:

  1. Turn off the power and gas.
  2. Disconnect the electric wires from the old valve.
  3. Use a wrench or pliers to remove the old valve.
  4. Install the new one, reversing the steps.
  5. Reconnect the wiring and turn on the power and gas.

However, note that different models may have different procedures. Refer to the owner’s manual before you begin.

Replacing a bad gas control valve requires experience and tools. Safety should be the priority. If unsure, hire a professional.

Maintenance of your Rheem can prevent such issues. Yearly inspections help professionals detect concerns early.


Code 12 error in a Rheem tankless water heater? Serious stuff! Don’t ignore it, as it can result in your heater shutting down completely. Uncomfortable and inconvenient.

First step? Check the gas supply and venting for blockages or damage. If that doesn’t work, call a professional. To stop this from happening again? Regular maintenance. So don’t let your comfort at home suffer, get the issue fixed ASAP. Enjoy the peace of mind that comes with having a working water heater!

FAQs about Rheem Tankless Water Heater Code 12

What does Rheem tankless water heater code 12 indicate?

Rheem tankless water heater code 12 indicates insufficient hot water. This error stops the tankless unit from providing hot water as a safety measure and to prevent system damage.

What are the possible causes for Rheem tankless water heater code 12?

The possible causes for Rheem tankless water heater code 12 include low water pressure, clogged filter, faulty thermostat, improper gas pressure, dirty flame sensor, filthy flame rod, clogged venting, bad regulator, and too small gas lines.

What should I do if my Rheem tankless water heater frequently gets code 12?

If your Rheem tankless water heater frequently gets code 12 indicating insufficient gas, you should check the gas and power supply, clean or replace the flame rods, improve the airflow, and replace the bad gas control valve.

Why does my Rheem tankless water heater get code 12 only when the dishwasher is running?

If your Rheem tankless water heater gets code 12 only when the dishwasher is running, it could be due to a gas-related issue. One possible cause could be a dirty flame sensor, which can be fixed by cleaning it.

How can I fix Rheem tankless water heater code 12?

You can fix Rheem tankless water heater code 12 by checking the gas and power supply, cleaning or replacing the flame rods, improving the airflow, and replacing the bad gas control valve.

Is Rheem On Demand Water Heater particularly prone to Error Code 12?

Yes, Rheem On Demand Water Heater is particularly prone to Error Code 12 due to its complex repair system. It requires a functioning ignitor coil, flame sensor, flame rod, gas valve, and sufficient gas flow for a flame to be produced.

SmartHomeBit Staff