Troubleshooting Rinnai Tankless Water Heater Codes (10,11 & 12)

If you have a Rinnai Tankless Water heater, then you have an advantage when it comes to figuring out what is wrong with a malfunctioning water heater.  You can check error codes on the thermostat to narrow down the problem for you. This does you no good, however, if you don’t know what those codes mean.

Three common error codes you will see with Rinnai Tankless Water Heaters are codes 10, 11, and 12.  Code 10 indicates that there is a problem with the air supply, code 11 with the ignition, and code 12 with the flame. These codes will help narrow down what you need to repair to get your system working correctly.

Despite the help that these codes give you, you may still have to run through a number of tests before you find the reason for the error code. Knowing where to look and the more common reasons for those error codes will save you time in getting your system up and running again.

Error Code 10 

Rinnai error code 10 means that there is something wrong with the air supply, exhaust system, airflow, or flue pipe.  Rinnai error code 10 is tied to the air pressure sensor that measures airflow. This code is found on all Rinnai tankless water heaters, as well as Sensei series models.


Your Air Intake is Blocked 

In order to function correctly, gas appliances, including Rinnai tankless water heaters, need air in order to combust. If the air intake is blocked, then there can be no combustion.

One of the issues can be a dirty air filter.  Air filters eliminate lint, dirt, and other forms of debris from entering the system.  Over time the air filters get clogged, which prevents air from entering the system.

The air intake can also be blocked by other blockages. It may be possible to clear this code by cleaning out all the dirt, carbon, mineral buildups, and debris from the internal elements.

The Flue is Blocked 

A flue is the water heaters venting system. When combustion occurs within the water heater, it creates waste gases, including carbon monoxide. The gases are then expelled through the flue, which is vented out of your home.

A code 10 on your Rinnai tankless water heater can mean that your flue is blocked or that it was not installed correctly. One of the ways to check to see if the problem is with your flue is to disconnect the pipe and turn the water heater on. If your water heater is still giving you a code 10, then the problem isn’t the flue.

Error Code 11

A Rinnai error code 11 means that there is a problem with the ignition in general.  Fixing an error code 11 will require an understanding of how the water heater works and all the interior components. In other words, fixing this error will not be quick or easy – it will require a professional to handle it.


Trouble With the Ignitor

The most obvious source of an ignition problem is the igniter. However, the issue may not be as easy to identify, since there could be a number of problems wrong with the ignitor.  

There could be a spark issue with the ignitor stemming from bad connections.  If the igniters are loose, they can also cause a short. Another issue can be dirt or carbon buildup on the ignitor.

Any of these issues can cause the igniter to malfunction. In order to fix these issues, you should check to see if the ignitor is secured and free of carbon or dirt.

Problem With the Gas Supply 

If the problem is not found with the ignitor, another natural place to look is the gas supply. Here, too though, there are a number of ways that this can be an issue.

If there is no gas reaching the water heater, there can be no combustion because there is no fuel. If gas is making it to the water heater, there may be an issue with gas pressure problems. If the problem is gas pressure, then there are probably bigger problems going on with the water heater.

Servicing this error requires experience with gas supply. If you do not have experience in this area, contact a professional.

Wrong Wiring on the Flame Rod

A flame rod is the part of a water heater that is used to detect whether there is a flame. When the flame is on, the rod is energized and creates a charge that completes the circuit. If the flame is not detected, then the valves are closed so that gas cannot escape.

If error code 11 pertains to the flame rod, it could be a problem with the wiring. You can check to see if there are loose connections with the wiring; if so, they need to be secured. You can also check to see if there is any build-up or dust on the flame rod which can also cause issues.

Lack of Vents

A code 11 can mean an inability for the system to properly vent the heat.  This can restrict airflow, and it can also cause a build-up on the flame rods. If this is the case, then you may want to check the flame rod to ensure that there are no issues there as well.

The way that this can be cleared is to check the water heater’s vents for any blockages. If there are blockages, then they should be cleared. You should also check to make sure that the vents were properly installed and that nothing is obstructing the vent.

Excess Moisture 

Condensation on the unit can cause any number of issues with water dripping into the unit and causing corrosion on the components. In the case of a code 11, it is possible that the damage is either with the condensate drain line or in the drain trap. 

Check to make sure that the lines and drain trap have been installed correctly.  In addition, check inside to see if water is dripping into the unit. If there are leaks, secure them by tightening attachments or replacing components.

Also check the electric board. Water on this board may cause malfunctions, which means that it will need replacement.

Error Code 12 

Rinnai error code 12 on the tankless water heater means that there is “no flame”. This can mean that there is no flame in the combustion chamber, among other things. The most obvious source of the error may be the flame rod, but there are several other potential sources for flame failure.


Incorrect Gas Pressure

One of the problems with creating a flame is the lack of gas pressure. If the gas pressure is not correct, the pilot will flicker and the ignitor will not start.

If there is an issue with incorrect gas pressure, then it is possible that the gas control knob or the shutoff valve is not set correctly.  If they are correct, then the problem may be with the type of gas that is being used.

Rinnai tankless water heaters take natural gas or propane. If this is not the type of gas being used, then it is possible that this is the source of the problem.

Your Gas Burner is Clogged

Another source of an error code 12 is the gas burner being clogged. Once again, check your gas valve shut off and the gas control knob. Also, ensure that all the gas pipers are open and make sure that there is gas in the tank. 

It is also possible that your gas tank system is the incorrect size or that it does not meet the specifications required by your water heater. You can check the specs on the label on your water heater to see if the gas system works with your water heater.

The final possibility is air in the gas line. If there is air, it must be purged from the lines.

The Fan is Clogged

A code 12 on a Rinnai tankless water heater can also refer to the fan blower being clogged. If the fan blower is clogged, then the gas in the water heater cannot burn clean, nor can the exhaust be removed. In order to clear this issue, the fan has to be cleared of dirt and debris. 

The best way to clear the fan is to use a cloth and compressed air to blow off any accumulated dust. You can take a shop vac or a regular vacuum with a hose and nozzle attachment to help you suck this debris out of the system.

Improper Venting

One commonality that error codes 10, 11, and 12 all share is that they can all be set off by improper venting. But for code 12, the primary cause is improper installation.

If the venting systems have any parts used that are not approved by the manufacturer, or if there are any parts that do not meet manufacturer specifications, then code 12 may appear.  

In order to clear this code, the venting (and the unit installation in general) should coincide with all specifications laid out by the manufacturer. It is recommended that you use a qualified technician to make sure that this is the case.

Your Flame Rod is Damaged

A flame rod that is damaged or disconnected is one of the most common reasons for a code 12. The flame rod should be checked to ensure that it is working correctly and that it is properly connected.

The flame rod should be free of carbon buildup and other residues. If it is not, you can use fine-grit sandpaper to clean it off.

The flame rod’s wires should have no breaks or other signs of damage and must be firmly inserted into the bracket mount. You can ensure that everything is functioning correctly if the flame contacts the flame rod and it is blue in color without flickers.  

When Should You Call a Professional

Some of the issues covered by the codes above can be handled by the homeowner directly. However, in cases such as with code 11, the issues involved will require the services of a professional to handle. 

Simple maintenance on water heaters can make for easy DIY projects that are fairly inexpensive. Water heater components typically cost less than $50, with a few exceptions.

If you must call in a professional, you will end up spending between $45 and $150 for labor. The national average cost of repair for water heaters is just under $600, with a low of $200, and a high of $960.  

If you cannot fix the problem on your own, then professional help is warranted.  That said, water heaters are expected to last an average of 10 years, and if the cost of repair is more than $1,000, it may be worthwhile to consider getting a new water heater.


A Rinnai tankless water heater can save you time in finding the problem and can help you avoid a costly bill after calling in a service technician to diagnose the problem. By checking on your water heater and giving it some regular maintenance personally, you can also familiarize yourself with the system and avoid these codes coming up in the future at all.

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