Rheem Tankless Water Heater Error Code H103

Rheem Tankless Water Heater Error Code H103

Rheem Tankless Water Heater Error Code H103 means the high-limit safety switch gets tripped. This safety device will shut off your tankless water heater automatically when the water temperature gets too high. 

To reset the error code H103, you should check the high-limit switch and replace it if required. Apart from this, check the burner for blockage and flush the unit. 

Below, I will walk you through a step-by-step guide to erase the fault code H103. 

How To Fix Rheem Tankless Water Heater Error Code H103?

As I mentioned earlier, a tripped high-limit safety switch is responsible for the error code H103. Check the switch electrically. If you get no reading, you should replace the high-limit switch. 

Let’s see how you can inspect the high-limit switch electrically: 

1. Turn the unit off and detach it from the electric connection.

2. Unscrew the front access panel to access the high-limit switch. You can find the high-limit switch on the top middle of the unit: 

high-limit switch on rheem tankless water heater

3. Disconnect the high-limit switch wire connectors and get your digital multimeter to check the resistance of the high limit switch. If there is no resistance, I bet the high-limit switch is at fault. In this case, you need to replace the high-limit switch. 

Replace the high-limit switch with a new one and turn on the unit. I hope it will help you reset the error code H103. 

How To Reset Rheem Tankless Water Heater?

Once you replace the high-limit switch, it’s time to reset the tankless unit. Go along with these steps to reset the water heater: 

  • Turn off the unit by pressing the power button on the remote control.
  • Disconnect the water heater from the electric connection by unplugging the power cord.
  • Leave the unit for 30 seconds.
  • Restore the power to the unit and turn on the water heater by pressing the power button. It will reset your tankless water heater. 

How To Maintain Your Rheem Tankless Water Heater To Avoid Functional Problems?

Perform periodic and regular maintenance workflow to keep your water heater functional. 

Your tankless water heater will keep tripping the high-limit switch if the water temperature gets too hot. Generally, a dirty burner causes the unit to function intermittently. 

So, check the burner periodically and clean it if required. You can watch this video to learn how to clean the burner: 

Next, your water heater gets clogged by minerals and deposits coming with your supply water. When the unit gets clogged, it will heat the water intermittently and trigger the high-limit switch. 

To resolve this issue, you should flush the tankless water heater once a year. On the other hand, if you live in a hard water area, flush the unit every six months. 

Fortunately, I published an article on Rheem Tankless Water Heater Maintenance. Read that article to learn how to flush the water heater like a pro. 


What is Rheem code 10?

Rheem code 10 means abnormal low-rate combustion. To reset this code, ensure the vent component connection is secure and the air intake filter is clean. 

What is the error code 13 on a Rheem water heater?

Error code 13 on a Rheem Water Heater indicates a problem with combustion. It occurs due to a dirty water inlet filter, clogged burner, and dirty combustion sensor. Read this article on Rheem Tankless Water Heater Code 13 to learn how to reset this code. 

What are the codes for the Rheem water heater?

Rheem Water Heater may throw several error codes, including 10, 11, 12, 13, or 29. To get the full list, check out this article: Rheem Tankless Water Heater Error Codes


A tripped high-limit safety switch is what triggers the error code H103 on your Rheem Tankless Water Heater. When the water temperature gets too hot, the unit will shut off itself and trip the high-limit switch. 

To fix this issue, replace the high-limit switch. Besides, check the burner for blockage and clean it as it could cause the water heater to heat water at high temperature. Lastly, flush the water heater once a year or twitch to avoid such operational probal. 

You can also hire a professional or contact the Rheem Support Team if you fail to resolve this issue by following this guideline. 

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