Brand guide
A.O. Smith Error Codes: Meanings & Safe Checks
Match the equipment family and displayed code before following any check.
The official ATIO 910 Service Handbook identifies 031 as incorrect dipswitch settings.
A.O. Smith water heater 1 flash means Low flame signal; the control continues to operate.
The official ATIO 910 Service Handbook identifies 101 as abnormal combustion. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 111 as ignition failure. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 121 as flame loss. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 2 flash means Pressure switch failed closed. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 3 flash means Pressure switch failed open. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 311 as output thermistor fault.
The official ATIO 910 Service Handbook identifies 321 as inlet thermistor fault.
The official ATIO 910 Service Handbook identifies 331 as mixing thermistor fault.
The official ATIO 910 Service Handbook identifies 391 as air-fuel ratio rod failure.
A.O. Smith water heater 4 flash means ECO (Energy Cut Off) limit thermostat temperature limit was exceeded; the main burner is shut off.
The official ATIO 910 Service Handbook identifies 441 as flow sensor fault. See the verified model scope, safe checks, and official source.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies 45-0 as upper or lower temperature probe short condition.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies 48-0 as upper or lower temperature probe open condition.
A.O. Smith water heater 5 flash means Flame out of sequence sensed. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 510 as abnormal main gas valve.
The official ATIO 910 Service Handbook identifies 551 as abnormal solenoid gas valves.
A.O. Smith water heater 6-1 flash means Retry limit exceeded (failed trial for ignition).
A.O. Smith water heater 6-2 flash means Recycle limit exceeded: pressure switch/high limit opened.
A.O. Smith water heater 6-3 flash means Recycle limit exceeded: flame lost. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 6-4 flash means Recycle limit exceeded: flame out of sequence.
The official ATIO 910 Service Handbook identifies 611 as abnormal fan motor. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 631 as pump failure. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 651 as abnormal flow adjustment valve.
The official ATIO 910 Service Handbook identifies 661 as bypass valve fault. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 681 as external fan mode failure.
A.O. Smith water heater 7 flash means Flammable Vapor Sensor (FVS) lockout. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 701 as computer board fault. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 721 as false flame detection. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 741 as main remote control problem.
The official ATIO 910 Service Handbook identifies 761 as communication failure. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 8-1 flash means Flammable Vapor Sensor fault detected. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 8-2 flash means Temperature sensor fault detected. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 8-3 flash means Electronics fault detected. See the verified model scope, safe checks, and official source.
A.O. Smith water heater 8-4 flash means Valve fault detected. See the verified model scope, safe checks, and official source.
The official ATIO 910 Service Handbook identifies 991 as abnormal combustion. See the verified model scope, safe checks, and official source.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A6-501 as low gas pressure.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A7-1201 as blocked air intake.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A8-1201 as blocked exhaust.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A9-17B as flame sensor detected flame when the gas valve should be off.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies B2-70 as ignition failure; flame not detected.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies CC-B as powered anode shorted to earth ground or the tank.
The official BTR 500 Service Handbook identifies continuous flash as flame sensed out of sequence for more than five seconds without the gas valve being…
The official BTR 500 Service Handbook identifies continuous on as internal ignition-control-board failure.
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies D6-8 as no water detected by the powered anode.