Rheem tankless water heater error code 12 is diagnostic information from the controller indicating flame failure in the system. This is caused by a variety of factors, including:
- Broken or disconnected flame sensor rod
- Insufficient gas supply
- Blocked venting
- Defective gas control valve
- Dirty combustion chamber
- Or, bad PCB
Whenever you see this error code, inspect the flame sensor rod for carbon build-up. If so, clean and adjust it properly. Next, ensure there is sufficient gas and air flow to the unit to ensure fluent burning. If the problem persists, it is more likely to require a specialist to take a look.
Before that, it’s worth visiting this guide till the end as I am going to share my years of experience using and dealing with the Rheem tankless water heater.
Let’s dive right in!
Table of Contents
What Is Error Code 12 On Rheem Tankless Water Heater?
As you’ve already come to know Rheem tankless water heater code 12 is the indication of flame error in the system. That means there is no flame in the unit or the controller isn’t recognizing the flame in the combustion chamber.
For this instance, a dirty or defective flame sensor rod is the big culprit. But at the same time, it may not be the actual source for this issue, even though there is more to it.
Error code 12 may display when there isn’t a gas supply to the unit. Here the flame error starts when the unit fails to meet the minimum requirements for gas.
Also, the flame failure indicates a lack of airflow, a blocked combustion chamber, improper grounding, or any bad wiring harness to the gas valve and PCB.
Possible Reasons For Rheem Tankless Water Heater Error Code 12 [Quick Overview]
First off, let’s go through this table summarizing all the probable reasons for Rheem error code 12 with their corresponding fixes.
| Probable Reasons | Recommended Fix |
| Dirty or broken flame sensor rod | Clean the sensor rod. If needed, replace it. |
| Gas Supply Interruption | #Ensure the use of correct gas type, gas pressure, and gas volume for your water heater. #Also, make sure the gas line, meter, and regulator are sized to support the BTU load. |
| Clogged exhaust venting | #Clean out all the blockages from the air intake and venting system. #Ensure the correct installation of the ventilation to your water heater. |
| Bad gas control valve | Replace the bad gas valve. |
| Dirty components | Clean out the burner chamber and blower motor properly. |
| Bad wiring harness to the PCB | Fix the bad wiring or replace the defective control board. |
How Do I Fix Error Code 12 On A Rheem Tankless Water Heater [7 Easy Solutions]
Well! After previewing the quick overview, certainly, you’re certainly wondering about the detailed troubleshooting. Here is all for you highlighting all the responsive factors for Rheem error code 12 in detail and how to solve them effectively.
1. Dirty Or Broken Flame Sensor
In case of flame failure on a tankless water heater, a broken or malfunctioning flame sensor rod is the first culprit to blame. Either the sensor rod is disconnected from its place or clogged up with the carbon buildup.
The flame sensor rod is the most essential device in the system that is designed to convert the heat from a burning flame to a small current and send it to the control board. When the control board finds a signal that there is the presence of heat from the flame, it continues the heating process.
If there is a single malfunction from the flame rod and thus doesn’t get a signal from it, it leads to error code 12 Rheem tankless water heater on the control display.
Thus as for the first troubleshooting step, we’ll need to inspect the flame for any breakage or blockages. At least it needs to be cleaned to allow its operation to the maximum level.
How To Fix:
Before handling the heater inside, ensure your safety first. Disconnect your heater from the power supply. Also, turn off the gas and water supply to your water heater.
Now unscrew the attached screws on the top cover panel and remove it to access the flame rod. First off, head to the control board and locate the white “M” & blue “T” connectors of the flame sensor rod.
Cycle the unit on and measure the AC volts of that connector. It should give a reading in 1 – 100 AC VOLTS. If the voltage is Ok, activate the Maintenance mode on the display and it will show 05 for indoor models and 01 for outdoor models.
If not, be sure the flame sensor is malfunctioning and needs your attention. To do so:
i) Locate the flame rods just next to the burner, attached with 2 wires in each as shown in the picture below:
ii) Take off the electrical connection by pulling it off and unscrew the nut with a socket or flathead screwdriver. Now slowly pull down the sensor through the porcelain cover.
iii) Avoid touching the thin metallic rod with your finger, simply take a fine grit paper and cloth and clean the deposits. When done, put it back in place.
iv) In case of a broken flame rod, you need to replace it with a new one. Contact a professional one for Rheem flame sensor replacement.
2. Gas Supply Interruption
If there is okay from the flame sensor rod and still there is the same error code on the display, I bet your unit is running through an interruption in fuel supply. That’s the same case I also encountered while dealing with this code in my gas operated tankless system.
In general, a gas tankless water heater needs a steady and uninterrupted fuel supply to run efficiently.
But the higher possibility is you may not get sufficient fuel in your heater system which is causing flame failure and Rheem code 12 tankless water heater.
Now in case of a gas supply interruption, here are a few major factors that you need to concentrate on:
i) Improper Gas Type
The first and basic mistake that most users make is the use of the wrong type of fuel for their tankless system. If it is a gas tankless water heater, then you need to make sure to use the correct fuel.
Usually, there are two types. One is propane and the other one is natural gas. Go through the manual for your Rheem tankless water heater and ensure the right type of fuel.
ii) Insufficient Gas Pressure
The second major fact that you need to concentrate on is the correct gas pressure. In this instance, first off, make sure there is sufficient fuel in your LP tank. And the gas supply is not being cut off if you’re operating a natural gas tankless water heater.
Once done, take a pressure gauge and measure both inlet and manifold gas pressure for your water heater.
How To Fix:
If you have propane fuel, you should get a minimum 11″ WC and a minimum 5.3″ WC for natural gas. Now in the case of manifold pressure, the natural gas should be at 2.52+ fan pressure and 7.36+ fan pressure (WC) for LP gas.
If not, adjust the gas pressure properly to power up your water heater
iii) Blockages & Leaks In The Gas Supply Line
When there is not sufficient fuel supply in the heater, then you might have a blockage in the gas supply line and pipes. If so, you need to clean it. In case you are suspecting air in the gas line, bleed it to get uninterrupted gas flow.
When done, now check for a gas leak in the supply line. Especially inspect the gas regulator to check for leaks. Replace the bad pressure regulator if needed.
iv) Undersized Gas Line For BTU Load
It’s crucial to ensure that the gas pipe size is enough to support the BTU load of your water heater. Undersized or too small a gas pipe size will cause incomplete combustion and an increased pressure drop and flame failure in the system. That results in code 12 tankless water heater on the remote display.
As for the fix, check the gas line size to ensure that it can support the BTU load. If not, you need to resize it. For instance, we’ll recommend contacting a qualified technician to handle the task.
3. Clogged Exhaust Venting
Insufficient airflow in the unit due to improper venting is one of the most frequent reasons to blame in the case of Rheem tankless water heater error code 12. If it is a gas-operated Rheem tankless water heater, proper ventilation is quite essential to escape the combustion gas from the system.
Blockage in the ventilation will easily cause recirculation if exhaust gas back into the unit. That results in carbon buildup in the flame rod and spark electrode leading to flame failure.
When exhaust gases come from the back, you will easily identify the fact by the reddish-yellow burner flame with an unstable pattern.
How To Fix:
First off, inspect the air intake and exhaust for any blockages. If so, take a vacuum cleaner with an extension attached and suck up all the stuck debris. If needed, you may use a plumbing snake and release the blockage.
When done, check the venting material, size, termination, and length to ensure that all are meeting all the instructions according to the manufacturer.
It’s better to contact a qualified service technician to install the ventilation system of your tankless water heater properly.
4. Open Or Short Circuit On Gas Valve
The error code 12 on the Rheem tankless water heater may display if there is an open and short circuit on the gas valve of the system.
The control valve on a tankless water heater is mainly designed to regulate the gas flow to the unit. In case it gets defective or stops operating, there will be a distraction in the gas flow operation throughout the system.
Now if there is no gas flow in the ignition chamber, there will certainly be no flame that leads to error code 12 in your Rheem tankless water heater.
How To Fix:
Before considering the gas control valve defective, inspect the control valve wiring harness for loose or damaged terminals. Usually, it is located on the lower right side of the unit.
Also, check for proper voltage to the gas valve wiring to the control board. For instance, remove and reinsert connectors “K” & “R” on the control Board. Now, measure the DC voltage across the different wiring connections.
If needed, replace the bad gas control valve.
5. Dirty Components
Clogged components of the Rheem tankless water heater are one of the big reasons for triggering error code 12 on the remote display. Such as, when there is dirt and debris in the combustion chamber, certainly the gas won’t burn clean and the exhaust gases fail to safely vent out of the system.
Rheem tankless water heater equips many delicate components that are sensitive enough to condensation, contaminants, and buildup. That includes an exhaust vent, air intake, combustion chamber, or fan blower.
We’ve already cleared out the air intake and exhaust vents for proper combustion. Now, we’ll inspect the combustion chamber and burner to ensure the clean burning of the gas and remove the error code 12 on the control display.
How To Fix:
First off, make sure you have unplugged your tankless water heater from the power outlet. Now remove the front cover panel and remove the screws that are holding the PCB. Allow PCB to hang by wires.
Now remove the retaining clips and screws holding the burner plate cover. When done, gently pull off the cover plate.
Remove the rubber grommets and pull them straight out on both sides of the burner assembly to slide them out of the chassis. Take a compressed air and blowback down through all burner ribbons.
When done, inspect the blower motor for any blockages or damages. If so, clean it using compressed air as well.
Test the blower motor manually and ensure the fan blade is tight on the motor shaft and spins freely. If needed, replace the bad blower motor.
6. Improper Grounding
If still you have the same error code 12 on your Rheem control display, the best chances are the unit is not properly grounded. Though your tankless is gas operated, it needs an uninterrupted power supply as well to turn efficiently.
How To Fix:
To ensure proper grounding, locate the green ground wire connections on the lower left side of the PCB. Visually inspect the connection for any cracks and damages.
Tighten the loosen connection and replace the bad one. Also, make sure the ground wires of your unit are connected properly.
7. Bad Wiring Harness On PCB
Last but not least, malfunctions from the PCB is one of the main reasons for triggering error 12 on the Rheem tankless water heater remote display. Chances are you have a bad wiring harness to the PCB and the control board is defective itself that needs replacement.
How To Fix:
Disconnect and reconnect all the wiring connections to the control board. Tighten the loosen wires and replace the damaged wiring harness. If needed, you may need to replace the bad control board.
FAQs:
What does Rheem tankless water heater error code 11 mean?
Rheem tankless water heater code 11 is the error indication of the ignition failure in the system. Check the gas valve to ensure that it is turned on all the way. Also, the spark electrode should be operational.
Why is my Rheem tankless water heater not getting hot enough?
Rheem tankless water heater no hot water is mainly related to the incorrect temperature setting, wrong adjustment of the anti-scald valve, frozen water piping, or too high water flow rate.
Why is my Rheem tankless water heater beeping?
Rheem tankless water heater will beep mainly to inform you of the internal leakage in the system. Also, it occurs when there is high build up of limescale, incorrect water flow rate in the unit, or due to system overload.
In Closing
Rheem tankless water heater error code 12 is a clear sign of flame loss. Either the system isn’t detecting a flame or the flame is being extinguished during operation.
Various factors can contribute to this error code starting from the dirty flame sensor, wrong gas supply, insufficient air flow, or the bad wiring connection to the electrical component.
Fortunately, we’ve highlighted all the above factors throughout our Rheem tankless water heater code 12 fix guide with effective solutions. Follow our instructions from first and end and hopefully, you will be able to clear the code effectively from your remote display.
While in operation, if you encounter any more different codes on your Rheem remote display, you can check out the comprehensive Rheem tankless water heater error code guide to fix the error like a pro!