How To Clean The Flame Sensor On A Rheem Tankless Water Heater [Step By Step Guide]

Rheem tankless water heaters are quite effective at providing hot water when it is needed. However, it stops working properly if the flame sensor becomes dirty. Want to know how to clean it? You are on the right page! We’ve sifted through the internet and researched the answer to share with you.

The step-by-step procedure for cleaning the flame sensor on a Rheem tankless water heater is the following:

  1. Turn off the unit's power supply.
  2. Turn off the water and drain the unit.
  3. Remove the access panel cover of the unit.
  4. Locate the flame sensor.
  5. Detach the flame sensor.
  6. Clean the flame sensor.
  7. Return the flame sensor.
  8. Return the panel cover of the unit.
  9. Turn on the unit.

In this article, we'll go into more depth regarding the flame sensor, including a thorough explanation of each of the aforementioned procedures. When replacing or repairing the flame sensor, we may compare the costs between doing it yourself (DIY) and hiring a pro. For more details, keep reading.

hand-rotate-temperature-adjuster-water-heater, How To Clean The Flame Sensor On A Rheem Tankless Water Heater [Step By Step Guide]

How To Clean The Flame Sensor On A Rheem Tankless Water Heater?

The flame sensor on a Rheem tankless water heater will become contaminated if it has been around for a while due to carbon or dirt buildup. Its probe stops detecting the flame when it becomes coated in carbon deposits. 


However, inspecting the flame sensor doesn't cost much money or take a lot of time. A simple solution to this problem is to clean the flame sensor and below are the steps you may follow.

1. Turn Off The Unit's Power Supply

All tankless units are powered by electricity regardless the unit uses gas for heating. So, unplug the unit and shut off the circuit breaker in your home's main panel. 

If it is powered by gas, turn off the gas valve to cut the fuel supply of the water heater. Usually, the gas valve has a red handle which is used to regulate flow. Verify the handle’s position, it is turned on if parallel to the direction of the flow of the pipe. So, it is off if it is perpendicular to the pipe’s flow.

You know that the power supply has been entirely shut off if there is no air coming out of the exhaust vents on top of the appliance. This will not only avoid shocks but also stop the unit from heating on while you are working.

2. Turn Off The Water And Drain The Unit

While you're at it, turn off the cold water inlet pipe and look for water leaks. Utilizing the vent pipe, drain the water heater.

3. Remove The Access Panel Cover Of The Unit

To access the unit's interior components, open the metal plate cover by turning the knob on the lower right of the panel 90 degrees to the left and open it up. Verify that none of the parts has any obvious damage.

4. Locate The Flame Sensor


Find the flame sensor that is just directly in front of you. Otherwise, it's clearly visible right next to the gas line. Obviously, by its name, it's going to be near the flames.

It has a single wire connected to a white porcelain base that may have become yellow or brown due to the accumulation of dirt or carbon over time. The flame rods are directly inserted into the unit's control board and resemble L-shaped probes or pins.

5. Detach The Flame Sensor

First, pull the wire connector away from the terminal to detach it. You might need to pull firmly because the cable has a spade connector, which can occasionally become stuck. 

As you can see there’s a single nut or bolt right there where you remove the wire. Use a quarter-inch drive, socket, or flat-head screwdriver to remove the screw that is securing the sensor to the burner housing wall. Secure the screws in the safe place and pull out the sensor slowly.

Click here to see this screwdriver set on Amazon.

Importantly, you don't touch the top or probe of the flame sensor. You can only touch or hold on to the porcelain because the oils will deteriorate the flame sensor faster. 

6. Clean The Flame Sensor

With fine steel wool or emery cloth, remove carbon buildup from the flame sensor. Remember that the probe is fragile. It will become harmed if you rub it vigorously. So, use a soft cloth to clean away any debris or residues. 

Click here to see this emery cloth on Amazon.

The probe will likely be dull and blackish before you begin cleaning it but once you're finished, it should be shiny or not dull and silver in color. This way, it will help the flame sensor last longer as well as detect the flame better. It's time to replace the sensor if you're having trouble cleaning it. 

7. Return The Flame Sensor

So now you'll put the flame sensor back in. Just slide it in, you can't really mess this up because there is only one hole that helps to align the flame sensor. But before reinstalling the flame rods, make sure it is dry.

Then, put the spade/wire connector back and as you return it, you will hear a little click. If for some reason it doesn't feel tight on or feels loose, just squeeze a little bit on those ends to help it snug.

Click here to see this Rheem flame sensor replacement on Amazon.

8. Return The Panel Cover Of The Unit

After cleaning up the flame sensor, put the cover back on. Slides underneath and then push it flush. Turn the knobs 90 degrees to the right.

9. Turn On The Unit 

Turn the water back on to the system and turn the electricity back on to the appliance. Make sure that the thermostat is also turned on. When the gas solenoid valve fires, you should hear it click and the exhaust vent turn on. 

To start the unit running, turn on a faucet, hot water tap, or other water source. Soon after, a flame will start to show through the tankless unit's viewing capsule in the center. Your water heater is now back in service.

Below is a YouTube video that serves as a clearer demonstration.

How Do I Know If My Flame Sensor Is Bad?

Your unit's flame sensor may occasionally become damaged and malfunction. If you're unsure whether your flame sensor is acting up and causing issues with your equipment, look out for these typical symptoms:

  • Your tankless water heater turns on and then off after a few seconds.
  • The flame sensor seems rusted or dirty.
  • There are cracks in the sensor's porcelain.

Any one of the three symptoms will cause your furnace to run in brief cycles, which means it will turn on and off in a matter of seconds. This occurs because a clogged or damaged flame sensor won't detect heat and will tell the unit to turn off.

How Much Does It Cost To Repair/Replace Flame Sensor?


Flame sensors experience some degree of wear and tear over time. If the flame sensors are not working, the tankless water heater will begin to send an error code usually code 12 error, and shut itself down. 

This error code, like others on the device, prevents the unit from producing hot water for safety and to avoid system damage. When deciding whether to do a DIY repair/replacement or hire a professional, you should consider the following costs:

DIY Cost

You only need light grit sandpaper, steel wool, or emery cloth, which will cost you less than $5, if the only problem is a filthy flame sensor. 

The task of replacing your flame sensor is not challenging. You only have to repeat the previous procedures by turning off the unit’s power, removing the flame sensor from the assembly, and disconnecting the wires. Then, skip the cleaning process and proceed with mounting the new flame sensor.

For replacement, a new flame sensor will cost you around $10 to $100 depending on the model of your unit and whether you choose an original equipment manufacturer (OEM) or a universal part. However, the majority of flame sensors on the market are priced between $30 and $50.

Make sure to obtain the appropriate replacement part when changing your flame sensor. Once more, you should go to a local HVAC shop because most of them have flame sensors on hand.

Check the information about your unit inside the access panel if you're unclear about which part to purchase. Provide your unit’s brand, model, and serial number so they can recommend the best fit for your unit.

Pro Cost

If you will assign this matter to a professional, you must pay the repair company's minimum service charges, which range from $100 to $650. Also, if your flame sensor needs to be replaced, the price range for a new one is between $10 and $100.

Of course, the price will vary depending on who you hire and what kind of unit you have. To get a good idea of what to expect, always ask the contractor how much they charge and what is included in the price.

Do keep in mind that you will need to replace the flame sensor 2-3 times throughout the typical lifespan of your unit as preventive maintenance. So, if you know how to change the flame sensor yourself, you can avoid paying double or thrice the service price.



Cleaning the flame sensor or rod of your Rheem tankless water heater is an easy job that you can do by yourself with the help of the step-by-step procedures mentioned above. However, if you are not confident to do it or there’s something wrong happening while doing it, don’t hesitate to reach a professional.

To learn more about the tankless water heater, check them below.

Where To Install A Tankless Water Heater?

Rheem Vs Rinnai Tankless Water Heater – Which To Choose?


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