Rheem Tankless Error Code Troubleshooting

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Having a good digital display or wireless monitoring app can be a great way to identify issues with your Rheem tankless water heater as soon as they appear. You might at first find the error codes confusing, but they’re actually easy to learn. Below are some of the most common Rheem error codes and what they mean.

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Rheem tankless water heater troubleshooting doesn’t have to be a difficult thing. That said, there are some errors you can easily fix yourself and some which should be left to a qualified service technician.

Use your Rheem heater manual as a reference when performing any repairs, and make sure to use the technical support number (1-866-720-2076) whenever you’re unsure what to do.

Have a different tankless water heater brand that needs troubleshooting?

Rheem Tankless Water Heater Error Codes

Error Code 00
What it Means: Continual combustion for more than 1 hour - This unit isn’t designed to run continuously with the circulation system.

How to Fix: Turn off all hot water taps to reset the unit. You may also need to turn off or replace the circulation system.

Error Code 05
What it Means: Imperfect Combustion - The system is dirty or blocked.

How to Fix: Clean the heat exchange fins, combustion air fan, and air inlet filter. Check the ventilation system and vent openings for blockages or dirt and clean as needed.

Error Code 10
What it Means: A false flame has been detected.

How to Fix: Check to ensure all vent and heat exchange components are clean and properly connected. Make sure the flue inlet and exhaust are free of blockage. Additionally, make sure the proper vent materials were used.

Error Code 11
What it Means: There’s no ignition.

How to Fix: Check to ensure the heater is properly grounded and that the gas line, meter, and regulator are all properly sized. Check the gas solenoid for valves for short circuits and the igniter wiring harness for signs of damage. Bleed any air from the gas lines. Ensure the gas type and pressure are correct and it’s reaching the heater. Finally, check the igniter to ensure it’s functional.

Error Code 12
What it Means: Flame failure: The heater can’t maintain a flame.

How to Fix: Check for proper grounding and that the device is receiving gas of the right type and pressure.Examine the flame rod to ensure it’s connected and has no carbon buildup. Disconnect the remote control, PC board, and all wiring harnesses, then reconnect.

Ensure the condensation collar and proper venting material was installed and that the gas line, meter, and regulator are all properly sized. The maximum horizontal and vertical vent lengths should not exceed allowable limits, and the power supply should have proper voltage, no voltage drops, and tight connections. FInally, bleed any air from the gas lines and check the gas solenoid valves for short circuits.

Error Code 14
What it Means: There’s a fault in the Overheat Wrap.

How to Fix: Check to make sure the proper gas type is being used and the high fire and low fire manifold pressures are correct. Examine the heat exchanger for cracks or other openings, as well as air flow restrictions around the vent terminal and unit. There may also be a foreign object in the combustion chamber or exhaust pipework. Finally, Ohm out the safety circuit.

Error Code 15
What it Means: This is a boiling safety warning.

How to Fix: The cold water inlet pipe and inlet valve should be fully open. Also, check to ensure there’s no scale blocking the heat exchanger.

Error Code 16
What it Means: Over Temperature Warning - The heater has exceeded safe heat levels.

How to Fix: Check the combustion chamber, exhaust pipes, heat exchanger, and vent terminal for scale or blockages.

Error Code 21
What it Means: There’s a malfunction in the air intake filter switch.

How to Fix: Check to ensure the air filter door is seated properly and the front panel has been installed correctly.

Error Code 24
What it Means: There’s a malfunction in the operational switch.

How to Fix: Press the max button, then the min button to reset the switch. In the event this doesn’t work, you'll need to replace the PCB.

Error Code 29
What it Means: The heat exchanger output temperature is too low.

How to Fix: Clean the heat exchanger air inlet.

Error Code 31
What it Means: There’s a fault in the water inlet temperature sensor.

How to Fix: Check the sensor wiring for any damage and clean off any scale. Ohm out the sensor, replacing it if necessary.

Error Code 33
What it Means: There’s a fault in the outgoing water temperature sensor.

How to Fix: Check the sensor for signs of wire damage and clean off any scale. Ohm out the sensor and replace if necessary.

Error Code 34
What it Means: There’s a fault in the combustion air temperature sensor.

How to Fix: Clean any scale from the sensor and check it for damage. Make sure there are no restrictions to the air flow. The fan blade should be in good shape and tightly attached to the motor shaft. Ohm out the sensor and replace, if necessary.

Error Code 35
What it Means: The thermistor is incorrectly connected.

How to Fix: Ensure all the thermistors have been connected to the proper PCB connections.

Error Code 51
What it Means: There’s a fault in the gas inlet solenoid valve.

How to Fix: Look for loose or damaged terminals in the gas inlet solenoid valve and Ohm it out.

Error Code 52
What it Means: There’s a fault in the modulating solenoid valve.

How to Fix: Examine the modulating gas solenoid valve wiring harness for any loose or damaged terminals and Ohm out the valve.

Error Code 61
What it Means: Combustion Fan Failure - The combustion fan isn’t turning properly.

How to Fix: Check to make sure there’s no damage to the wiring harness or motor and all connections are tight. The fan motor should turn with minimal resistance. You may also wish to Ohm out the motor winding.

Error Code 71
What it Means: There’s a fault in the gas inlet solenoid valve control.

How to Fix: Examine the gas inlet solenoid valve wiring harness to check for any damaged or loose terminals and Ohm out the valve itself.

Error Code 72
What it Means: There’s a fault in the flame sensing device.

How to Fix: There is likely an issue with the flame rod. Ensure the wiring is undamaged and providing the proper voltage. Remove the flame rod and clean off any carbon buildup with sandpaper. Replace the rod, making sure it touches the flame when firing and there are no foreign materials getting in the way.

Error Code 76
What it Means: Communication error with remote control.

How to Fix: Make sure there’s no damaged or loose connections. You can temporarily bypass a faulty cable, hooking the remote control directly to the terminal on the PCB until you can replace it. In an extreme case, you may have to replace the remote control or PCB.

Error Code 79
What it Means: There’s a fault in the fan motor current.

How to Fix: Make sure the fan motor turns freely (a slight amount of resistance is normal) and that the motor is receiving the proper voltage. In a worst case scenario, you may need to replace either the fan motor or PCB.

Error Codes 80 and 81
What it Means: The gas cut-off has failed.

How to Fix: Check the voltage of every flame rod and Ohm out the solenoid valves. Replace the gas control valve, if necessary.

Error Code 82
What it Means: There’s a problem with determining the gas type.

How to Fix: Program the PCB for the proper gas type.

Error Code 99
What it Means: The flue is blocked.

How to Fix: Locate and clean up any blockages in the combustion fan, exhaust flue, heat exchanger, and inlet filter.

No Code
What it Means: Nothing’s happening when water flows through the device.

How to Fix: There are several possible causes for this issue. Ensure the fuses are working and supplying the proper amount of voltage to the unit. Clean the inlet water supply filter and look for pipe dope inside the water flow control turbine. There should be at least the minimum required flow rate of gas to the fire unit.

Another potential cause happens mostly with freshly installed units. Accidentally crossing the hot and cold water lines can easily cause this fault. Similarly, bleed over in current installations can create an error. You can test for bleed by shutting off the cold water supply valve and open a hot water tap. Steady flow is a clear sign of bleed over. You’ll need to contact a professional to fix the bleed issue.

Check out also complete Rheem Water Heater Manuals.

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  1. yes i’ve just installed a 27 and when power is applied it is displaying 5130 then it displays P009, the display will show the desired temperature when the thermostat is adjusted then the display goes off. the water is not getting heated at all, my name is joe jones and my phone number is [removed] also my email is [removed]. We contacted your 800 number for trouble shooting assistance at 4:30pm central time and they were closed. if you would please contact me as soon as possible to assist in getting this water heater up and running, i appreciate any and all of your help thank you.

  2. How to fix a P1 error code on. Rheem Pronto tankless water heater?? Replace the PRV? If yes, what if you cannot find the PRV anywhere in or outside your home?

    • P1 signifies not enough water flow to turn on the unit. All tankless units have a minimum flow rate which must be achieved before the water heater will start heating water. Often, low-flow showerheads or fixtures cause the problem so the aerators inside should be removed. Other solutions may be to clean out the inlet water filter on the water heater or turn down the temperature on the unit.

  3. My Rheem tankless won’t heat water during the heat of the summer days. It works normally once temperatures drop. The unit is in my attic and it easily gets 130+ up there during the day.

    Is there a fix or adjustment for this or do I just have to live with it?

    • I have a Rheem Electric Tankless Water heater also. It is a RTEX-27. I just got the same error code. Finding any information on this anywhere is difficult. Of course it is a holiday weekend and cant get anyone at Rheem to answer the phone. Did you figure out what it is?
      My thought is it a flow error. It wont alarm is a sink is turn on, or the shower. It only errors if the Tub is on.

  4. Just installed a Rheem retex-18 seems to be working great. I’m getting a +50 degree water temp rise when the unit is on. Which is what I expected from the chart on the box. However I occasionally see “E4” on the screen and occasionally see an “E5” – Where is the error code list and what do I need to do to correct these errors?

    • Had same issue with mine. Emailed Rheem and was advised E5 is:

      E 5 Error code | High Flow Rate
      If the LED control board is displaying an E5 error code the desired volume of water is too high to reach your desired preset temperature and you will need to slow down the Flow rate if needed .

      Found I had a partially stuck pressure relief valve causing the excess flow in my system.

  5. What does a code C4 mean on a Rheem Pronto, Model RUTG-74PVN, installed in 2004 mean? We turned water off, checked circuit breaker, let unit sit 10 minutes, press ON/OFF and panel read “120” meaning it was set. Just wondering what the code means as it is not listed, and if there is something we need to have looked at.

    • Was there a number after “C4”? Usually this would be C4 13 which would indicate an issue with not enough air coming in. You’ll want to call for service on this one.

        • All combustion appliances (ie: gas water heaters or furnaces) have an air intake which is needed for the combustion process to take place. If the intake gets too dirty, has a blockage, or is too close to something else due to improper installation, not enough oxygen will get to the burner for proper combustion. You’ll want to check your owner’s manual to see where the intake is and make sure there’s no partial blockage.

  6. I have a Rheem tankless RTG95DV installed 7 years ago. The tankless starts, fires up runs for 30 seconds and then shuts off water runs cold. The remote display is blank. No lights no message. What steps to troubleshoot do you recommend.

  7. I tried to find code 25 and you do not even show it. My gas company did not refill our LP tank and we ran it dry. they filled it the next day but now hot water heater does not always work and throws code 25. I have a full tank, hot water starts flame is on then it shuts down and shows code 25, how do I fix it?

  8. I installed a Rheem 18kw tankless and have gotten E 103 for the display.
    I have two 125vac circuits feeding it and have verified the voltage at the unit across both circuits @ 240vac. After Ecosmart sent me the 2nd replacement control circuit board replacement, the error -low voltage- has not changed. Ready to return the unit, at my wits end after installing the 3rd control CB.

  9. The remote control is dead, checked to see if Rheem Eco180XN3 has power reaching it and it does, when hot water is requested from the water heater, water heater activates but water comes out warm?

  10. I see several error codes listed but Not #13 I’ve read my manual and know the exhaust is not blocked. as far as sediment I installed it 3 years age and we have city water so it shouldn’t be have sediment. So my question is where do I go from here? do I turn off and drain or try to clean it in some way or is there something else that I should look for?


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