How to Troubleshoot American Tankless Water Heaters

Understanding the error codes and troubleshooting American tankless water heater. See how the diagnostic system helps you find the cause of the problem for easy repair.


Every tankless water heater from American is equipped with the diagnostic electronic system for better safety, convenience, comfort and easy troubleshooting. These units have the ability to check its own operation continuously and if any problem occurs, the diagnostic system will show the error code either on the temperature controller or remote control. The list of the error codes below will explain the cause of the problem and provide a solution.

Either the water heater does not ignite, water is cold or too hot, or the unit is making loud noise, the error code will be displayed, and the LED on the computer board will be ON.

The error codes will be shown differently in individual and multi-system setup. When two or more water heaters are installed within the Easy-Link system, the display will show not only the error code but which unit is having a problem.

I will assume that your tankless water heater was professional installed.

Error codes of the American tankless water heaters

Error Code 031 or 03

Check the DIPswitch setting on the electronic computer board if it is incorrectly positioned. The LED will be blinking one time.

Error Code 101 or 10

The LED flashes five times. You should check and remove any blockage in the venting system, and dirt in the burner and fan motor.

Error Code 111 or 11

The problem is with the ignition failure where the LED flashes three times. Check that the Hi-limit switch is correctly operating, there are no damages on the circuit board, there are no loose or damaged wires, and the flame rod is clean. There should be no leaking that can affect the proper ignition.

Error Code 121 or 12

This error code indicates that there is a loss of flame... the LED flashes three times. As with the previous error code, check that the Hi-limit switch is functioning, the wire connections are not loose or damaged and there is no water leaking.

Error Code 311 or 31

The outlet thermistor and heat exchanger failure (depends on the model). Check the connection between the wires and the thermistors and switches are clean of debris. The LED flashes two times.

Error Code 321 or 32

The inlet thermistor failure. The same action steps as with the error code 311. The LED flashes two times.


emergency plumber

Error Code 331

The outlet thermistor failure. The same fix as with the error code 311. The LED flashes two times.

Error Code 341

The exhaust thermistor failure. The same action steps as with the error code 311. The LED flashes two times.

Error Code 391 or 39

When there is an air-fuel ration rod failure, the LED flashes two times. Make sure that the connections are OK, and you have cleaned the air-fuel ratio rod from soot.

Error Code 441

The flow sensor failure, the LED flashes two times. Ensure that the connections are tight and there is no debris on the flow sensor.

Error Code 510 (or 51) and 551

Problems with the gas valve and solenoid valve. The LED flashes six times. Check the wires, connections and the computer board for damages.

Error Code 611 or 61

Problems with the fan motor. The LED is blinking four times. Check and fix wire damages, loose and corroded connections, remove dust in the fan motor and ensure the circuit board proper work.

Error Code 651

Four times LED blinking for the problem with the flow adjustment valve. Check for loose connections, wire damages, scale buildup and water leakage, repair or replace if needed.

Error Code 661

The LED flashes four times if there is a problem with the bypass valve. Inspect the bypass valve, wires and connections, potential scale buildup and water leak.

Error Code 701 (or 70) and 711

A problem with the computer board and the LED flashes once. Check wire connections and fix the damages.

Error Codes 721 or 72

The LED flashes six times. The error code indicates a false flame detection. Check is the condensate drain properly installed and there is no leaking from the heat exchanger.

Error Code 741 or 74

Problem in connection between the remote controller and the tankless water heater.

Error Codes 751

Problem in connection between the temperature controller and the tankless water heater.

Error Codes 761

Problem in communication between water heaters in the Easy-Link system. Check the connection between the parent and child unit.

Error Codes 941

LED is blinking five times and the problem is related to the high exhaust temperature on direct vent indoor models only. Check if the set temperature is higher than 140 F.

Error Codes 991 or 99

LED flashes five times. Since the problem is with the improper gas combustion check is the water heater installed for the recommended elevation of the region, is there a vent blockage, vents are on the recommended distance from each other and there is no dirt and debris in the burner or fan motor.

Things to consider

  • Minimum activation flow rate is approximately 0.6 GPM.

  • Max. temperature for residential applications is 140 F and 185 F if the commercial controller is used.

Thanks to the diagnostic system, troubleshooting American tankless water heaters is much easier and convenient than on models without the advanced electronics. Keep in mind that most of the problems mentioned above can be prevented if cleaning and maintenance are done regularly and per manufacturers' instructions. Also some of these problems are easy to fix while some require a service call.


Related Articles

Review, Ask and Comment

Enter Your Title

Home > American tankless water heaters > Troubleshooting American