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Learn about AO Smith tankless error codes for easy and inexpensive troubleshooting. The repair guide covers indoor, outdoor, condensing, non-condensing, and ultra-low NOx water heaters with on-demand technology.
Use the AO Smith code guide to find the main causes and solutions for the problems of the following models: 110, 310, 510, 240, 340, and 540 series, for safety, convenience, and great savings.
AO Smith tankless water heaters equipped with the remote controller have a great advantage; a self-diagnosing function that helps in diagnosing the heating problem. If there is a problem with the water heater, an installed remote will make a sound, and the error code will display on the screen. To have the unit working properly, it has to be supplied with the power and correct connection.
A guide to troubleshooting water heaters with the listed error codes below is useful for DIY homeowners, but our recommendation is always to get help from a qualified technician.
If the remote controller is not installed on the water heater, and there is a problem, the error codes will be shown differently. For example, a model 510 will display the numerical code on the 7-Seg LED on the computer board, while the 110 and 310 models only a blinking red LED that can flash one time or more. Models from the 240, 340, and 540 series will show the error codes on both temperature controller and remote controller.
We will assume that the tankless unit, before failure, was correctly installed (with the correct gas type), per the manufacturer's instructions and codes. The tools needed to solve the problems from below are mainly the screwdriver, manometer, and multi-meter.
To fix the tankless water heater from AO Smith properly and fast, we will show all three error codes (in the subtitle), the first for the units with the remote controller, the second for the units with the 7-Seg LED, and third are those heaters that do not have the remote... only blinking LED.
Problem: Incorrect dipswitch settings.
Solution: Check for the proper settings on the computer board.
Problem: Warning for the "991" error code.
Solution: Check for blockage in the vents, the distance between the intake and exhaust terminals is per instructions, and remove if there is grease or dirt in the gas burner and fan motor.
Problem: The ignition failure.
Solution: Check if the Hi-limit switch properly functions and that there is no loose or broken wire connections, no soot on the flame rod, or a damaged computer board. Can you hear a buzzing spark ignition from the burner or two clunk sounds from the gas valve?
Problem: Flame loss.
Solution: Check for the proper settings on the computer board.
Problem: Outlet thermistor failure.
Solution: Check if there is a loose or breakage in the wire connection or debris on the thermistor.
Problem: Inlet thermistor failure.
Solution: Debris on the thermistor, loose or broken wire connection.
Problem: Mixing thermistor failure.
Solution: Debris on the thermistor, loose or broken wire connection.
Problem: Exhaust thermistor failure.
Solution: See the error codes 331, 321, and 311.
Problem: Problem with the air-fuel ratio rod - AFR.
Solution: Check for the soot on the AFR rod, wire connection, and breakage.
Problem: Problem with the flow sensor.
Solution: Check the wire connection, wire breakage, and debris on the flow sensor impeller.
Problem: Abnormal gas solenoid valve.
Solution: Check for connection and wire breakage or computer board failure (burn marks).
Problem: Fan motor fault.
Solution: Check for connection/breakage of wires, corrosion or frozen connectors, fan motor covered with dust, burn marks on the computer board.
Problem: Flow adjustment valve fault.
Solution: Connections or wire breakage of the flow adjustment valve, scale buildup on the motor drive that gets locked, or there is water leakage.
Problem: Bypass valve fault (only model 540).
Solution: Connections or breakage of wires of the flow adjustment valve, scale buildup on the motor drive which gets locked, water leakage.
Problem: Problem with the computer board.
Solution: Check for connection and breakage of wires, burn marks on the computer board, and power supply to the unit.
Problem: Gas solenoid valve drive circuit failure.
Solution: See error codes 111 and 121.
Problem: False flame detection.
Solution: Check if the condensate drain is installed on the vent collar of the heater. Is there leaking from the heat exchanger?
Problem: Miscommunication between the water heater and remote controller.
Solution: Check if the remote controller is of the right type, also connections between the water heater and remote.
Problem: Miscommunication in an Easy-Link system.
Solution: Check the connections between water heaters.
Problem: Improper gas combustion.
Solution: Is the water heater set for the right elevation? Look for the blockage in the vent system and ensure if the distance between the intake and exhaust is not too small. Check if there are any foreign particles or grease on the gas burner and fan motor. Is the surrounding air contaminated?
Keep in mind that the error codes are shown differently if the units are connected through the Easy-Link System... it can be seen what the error code is and which unit has it.