[Fixed] Rheem Tankless Water Heater Code 12

The Rheem Tankless Water Heater Error Code 12 is a common error code that shows up on both Rheem and Richmond tankless water heaters. Like other fault codes on the unit, this one stops the unit from producing hot water for safety reasons and to prevent damage of the system.

Tankless Water Heaters are a great advancement in technology when compared to the traditional tank water heater systems. They are able to deliver hot water on demand with a high level of efficiency.

But better technology often means more complexity when you run into a problem.

As the repair costs rise, as home owners, we need to continue to get more skilled at fixing more advanced problems that occur with home appliances.

In this post, we will discuss what code 12 is and how to fix it.

Top 7 Causes of Error Code 12

 Your Rheem tankless unit requires a flame to function properly. In order for there to be a flame several components and conditions need to be in place.

Every tankless needs to have a working ignitor coil, flame sensor, flame rod, gas valve, sufficient gas flow

The Rheem On Demand Water Heater is particularly notorious for this issue

Let’s dig into each one of these issues

Bad Ignitor Coil

In order to get a flame, you need the ignitor coil on your unit to send a signal from the control board to the ignitor to turn on the flame to begin heating.

The ignitor coil is an electrical component that can wear out over time. Without a functioning ignitor coil the ignitor will not activate which means you will a flame loss.

To fix the the the ignitor coil, here are the steps I follow

  1. Shut off power to the unit
  2. Remove the front panel
  3. Locate the Ignitor Coil on the right side of the unit
  4. Un-attach the ignitor coil from its harness
  5. Replace it with a new one

Bad or Dirty Flame Sensor

The flame sensor is the component in your unit that that signals to the burner that there is a flame. A dirty flame sensor is usually the result of carbon deposits over several years on the unit. 

The good thing is that this is a simple and check problem to fix. On several customer calls, I have been able to save my customers time and money. But you can save even more by doing it your self by following these steps. 

  1. Locate the flame sensor. Depending on your model, it will be on right or middle section of the unit
  2. Unscrew the component from the harness that holds it in place
  3. Use an emery cloth to gently wipe it down
  4. Re-install the flame sensor and start the unit back up and press the reset button 

Bad or Dirty Flame Rod

The flame role is a metal component that is “L-shaped” and roughly 3 to 5 inches long. Just like the flame sensor, it is also gets dirty from carbon deposits.

I usually pull the flame rod out and check to make sure there are no defects. And then I turn my attention to cleaning it thoroughly using the cloth. I then place the flame rod back into its harness and then start the unit back up

Flame Rods are located in the middle left section behind panel cover

Bad Gas Valve

For water heaters that have Gas as the fuel type, a malfunctioning gas valve is something that may be causing Code 12

To test the gas valve, I turn the thermostat down to 0 degrees for 15 minutes, then I raise it back up to 120 degrees for 30 minutes. After that I flow water through the hot side of my faucet. 

If I don’t have any hot water, it is likely that I need to replace my gas valve. 

If this is the problem, Find the gas valve of your unit usually located in the front and center behind the front panel. Replace it by unscrewing the bolts holding it in place.

Restart the unit and you unit will begin functioning again.

Insufficient Gas Pressure 

If your unit is fueled by Gas as most are, you need about 200,000 BTUs per hour for your unit to function properly. But it is possible that you may not have sufficient gas pressure to power your unit. 

Gas supply issues

Poorly sized Gas Lines

Your tankless unit should gas line should be sized between 1/2 in and 3/4 inch. If your unit is not new, it is unlikely that the gas line is your problem. 

Bad Regulator

A faulty regulator will not provide sufficient gas to your unit, preventing the heat exchanger from performing optimally. There are safety shut-offs that prevent too much gas from being supplied to your unit.

Replacing the gas regulator is something I do not recommend you trying to do by yourself. 

What is Rheem Tankless Water Heater Error Code 12

Error Code 12 occurs when your tankless unit cannot detect a flame. First, check that the gas valve to the unit is open that that there is gas to you home. If there is sufficient gas, the problem is that your flame rods are dirty and need to be cleaned.

This fault is common in the Rheem On Demand Water Heater Models

When there is there is no flame in the tankless unit, the system shuts off for safety reasons. Without flame and gas supply turned on, the tankless system would be susceptible to damage or even a fire if there is an ignition or electrical malfunction.

This is why the unit creates a code 12 error and shuts itself down.

With the system shut down safely you can now begin troubleshooting steps.

How to Fix Rheem Tankless Water Heater Code 12

To fix Error Code 12, make sure that there is gas flowing to the system by checking that all gas valves are in the open position. Once verified, open up the front panel and remove the flame rods in the middle left side of the panel. Clean the flame rods and then reinstall them.

Step 1: Remove the Front Panel of the Rheem Tankless Water Heater Unit

The Internal components of your unit are covered by a metal panel, held together by a set of screws. Remove the screws to expose the internal parts of the unit. Make sure there is no visible damage to any of the parts.

Inside Rheem Tankless Water Heater Panel

Step 2: Shut off Power to the Unit

Every tankless unit is powered by electricity even if it uses gas for heating. Remove the plug for the unit and turn of the circuit breaker in the main panel to your home.

You will be able to tell that the power source is completely turned off because there will be no air coming out of the exhaust vents on the top of the unit.

Step 3: Shut off Water and Drain the Unit

Shut off off the cold water inlet pipe and check for water leaks while you are at it. Drain the hot water heater by relieving it through the vent pipe.

Step 4: Check that there is Gas supply to the unit

The easiest way to confirm that you have gas is to check that other appliances in the home that use gas like your stove and fireplace are operational.

The tankless heater itself has a gas valve that feeds it from the gas line of the utility company. The valve will have a red handle that controls flow. Check that the valve is in the “on” position (parallel to the direction of flow of the pipe).

Step 5: Remove and Clean Flame Rods

The flame rods are responsible for detecting that there is a flame on your Rheem tankless water heater. Over time, there can be dirt or carbon buildup on the sensors. The flame rods look like L-shaped probes or pins and are connected directly to the control board of the unit.

To remove the flame rods, unscrew the brackets that secure them to the burner assembly panel and carefully take them out.

Flame Rod Location once panel is open. Unscrew bracket holding flame rod.

Clean the rods with a paper towel and water. If the the dirt is more grimy, you can use some rubbing alcohol or acetone to clean them.

Make sure that the flame rods are dry before reinstalling them be reattaching the bracket back onto the burner assembly panel.

Step 6: Power Up The Unit

Once the flame rod is re-installed, turn the water back on the the system and power on the unit. Don’t forget to make sure that the thermostat is on as well.

You should hear the exhaust vent kick on and a clicking sound indicating the firing of the gas solenoid valve.

Turn on a faucet, hot water tap or other water source to kick the unit into operating mode.

Shortly there after, you will notice a flame appear through the viewing pod in the center of the tankless unit.

Your hot Water heater is Operational again.

Related Posts:

What is Richmond Tankless Water Heater Error Code 12

Error Code 12 on Richmond tankless water heater is the same as on the Rheem Tankless Unit. This fault codes signifies that there is a flame failure and that the tankless unit cannot power up as a result. Check that there is sufficient gas pressure unit. If so, remove the flame sensors and clean them.

Final Thoughts

The Rheem Tankless Water Heater Error Code 12 occurs when the flame sensor detects there there is no flame to the unit. The system shuts down in preparation for troubleshooting.

The first thing to check is that there is Gas supply to the unit. There there is no issue with gas supply, the problem is that the flame rods are dirty. Removing them carefully and cleaning them thoroughly will resolve the fault code and get your unit back in proper working order.