How to Troubleshoot American Tankless Water Heaters using Error Codes

Understanding the error codes and troubleshooting American tankless water heaters. See how a diagnostic system can help you find the cause of the problem for easy repair.

Every tankless water heater from the American manufacturer is equipped with an electronic diagnostic system for better safety, convenience, comfort, and easy troubleshooting.

These units can check their operation continuously, and if any problem occurs, the diagnostic system will show the error code either on the temperature controller or a 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, the water is cold or too hot, or the unit is making a 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 the single and multi-system setup. When two or more water heaters are installed within the Easy-Link system, the display will show the error code and which unit is having a problem.

I will assume that the tankless water heater was professionally installed.

List of error codes

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 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 should be taken as with the error code 311. The LED flashes two times.

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 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 codes 510 (or 51) and 551

Problems with the gas valve and solenoid valve. The LED flashes six times. Check the wires, connections and a 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 for the 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 codes 701 (or 70) and 711

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

Error code 721 or 72

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

Error code 741 or 74

The problem is in the connection between the remote controller and a tankless water heater.

Error code 751

The problem is in the connection between the temperature controller and the tankless water heater.

Error code 761

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

Error code 941

LED blinks 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 code 991 or 99

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

Things to consider

• The minimum activation flow rate is approximately 0.6 GPM.
• The maximum 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 advanced electronics. Remember 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.

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