How to Fix Rinnai Error Code 12 - Troubleshooting Tips

Rinnai tankless water heaterRinnai

An error code 12 is one of many Rinnai diagnostic codes used to identify problems in your Rinnai tankless water heater. It can be found on all models, including V, RU, RL, and RUR series.

Here is the list of the main causes of a Rinnai error code 12, also related to "no flame" and flame failure:

What is a Rinnai error code 12?

An error code 12 found on the Rinnai tankless water heater means "no flame" or a water heater didn’t recognize a flame in the combustion chamber. You can see diagnostic information on the control panel, where you set the temperature. If water is not equipped with the control panel, the same error code appears on the remote controller.

Error code 12 - Troubleshooting tips

While the error 12 is a flame error code, the flame rod is not the only culprit - there are several other reasons for the flame failure:

No gas supply

Check that all gas valves – on a water heater and gas pipes are open. If your tankless water heater uses propane, check if there is enough gas in the gas tank (cylinder).

Your gas water heater should get enough amount of gas. Use the specs (found on the label attached to your water heater) to see the proper inlet pressure and check if the unit meets the minimum required.

Sometimes, due to improper sizing, the gas system is undersized (smaller diameter and insufficient regulator), leading to a higher pressure drop than per specs.

You must contact a professional technician to fix the problem.

Improper gas type

Tankless water heaters can use either natural gas or propane. Make sure that your model is using the proper fuel type, per specs. 

Gas interruption

An uninterrupted gas supply is vital for the regular water heater operation. If the gas line has air in it, it needs to be purged. Hire a professional to bleed all the air from the gas pipes.

Disconnected or broken flame rod

Check the status of the flame rod and that it is properly connected. If the ceramic sleeve has cracks or is damaged, replace it.

The flame rod and the spark electrode (igniter) are firmly attached to the mounting bracket and should not be loose or misplaced. Some Rinnai water heaters have two and some, one flame rod.

Wires should be without any visible signs of damages or breakage and firmly attached to the rod and electronic board.

The flame rod must be in contact with the flame to function correctly. Check if the electrode gap is per specs. If the water heater is working properly, the flame should have a clear, blue color with a stable pattern. If the flame rod or spark electrode has deposits (carbon buildup), use the fine grit paper and cloth to clean or Scotch Brite pad.

Exhaust gas recirculation

Venting, together with the unit installation, should be done by a qualified technician or a plumber and must follow the manufacturer’s specs, instructions, and code.

An error code 12 might appear if the venting system has components not approved by the manufacturer, loose connections, or does not meet recommendations for the venting size, material, and clearances. If, for any reason, exhaust gases start coming back instead of going out, this can lead to improper gas combustion (yellow and red-ish burner flame, followed by the unstable pattern).

Dirty components

Ensure that the combustion chamber, fan blower, intake exhaust, and venting system are clean from debris and dirt so that gas can burn clean and exhaust gases removed safely outdoors.

Rinnai tankless heaters are equipped with several advanced and delicate components sensitive to condensation, contaminants, and buildup. Some homeowners suggested to using a shop-vac to suck out all the debris from the venting system.

Issues with electrical wires

Proper grounding is required. All the cables must be connected tight, dry, and with no damages. Check the components for electrical short.

Major component damages

As the main parts of the tankless water heater, the electronic board and a gas valve should be replaced if found defective.

Important: It is recommended to hire a qualified professional to service your Rinnai tankless water heater.

Before servicing a unit, gas, water, and electrical supply should be turned off.

How to display diagnostic codes

To display diagnostic codes, do the following:

  • Turn your Rinnai tankless water heater OFF.
  • Press and hold the ON/OFF button for a few seconds, and while holding, press the UP button.
  • You will see the last nine codes on display, flashing.
  • To exit from this maintenance mode, press and hold the ON/OFF button for a few seconds and press the UP button at the same time.
  • Resume the power by pressing the ON/OFF button again.

Testing a flame rod

It is worth mentioning that some live tests are required when the problem, such as an error code 12, appears.

With the water heater turned ON and running, place one probe of the multimeter to the flame rod, and the other probe to the ground, and you should get a reading between 5 and 150 volts (when measuring volts) or 1 amp (when the multimeter is set to Amps, and inline). 


It is important to understand that some error codes, such as the code 12, have some troubleshooting steps that are easy to follow and can lead you to problem-solving. In contrast, some other steps are hard and complicated and require calling a professional plumber or electrician.

Keep in mind that taking apart your water heater in search of problems and malfunctioning elements could be dangerous and void the manufacturer’s warranty.

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