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A.O. Smith Water Heater Error Codes: Meanings & Safe Checks
Choose the code exactly as shown. Meanings and reset procedures can change across model families, display formats and markets.
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1 flash A.O. Smith water heater 1 flash means Low flame signal; the control continues to operate. Search/display variants: 1 flash, 1flash caution 2 flash A.O. Smith water heater 2 flash means Pressure switch failed closed. See the verified model scope, safe checks, and official source. Search/display variants: 2 flash, 2flash caution 3 flash A.O. Smith water heater 3 flash means Pressure switch failed open. See the verified model scope, safe checks, and official source. Search/display variants: 3 flash, 3flash caution 4 flash A.O. Smith water heater 4 flash means ECO (Energy Cut Off) limit thermostat temperature limit was exceeded; the main burner is shut off. Search/display variants: 4 flash, 4flash stop-use 5 flash A.O. Smith water heater 5 flash means Flame out of sequence sensed. See the verified model scope, safe checks, and official source. Search/display variants: 5 flash, 5flash caution 6-1 flash A.O. Smith water heater 6-1 flash means Retry limit exceeded (failed trial for ignition). Search/display variants: 6-1 flash, 61flash caution 6-2 flash A.O. Smith water heater 6-2 flash means Recycle limit exceeded: pressure switch/high limit opened. Search/display variants: 6-2 flash, 62flash caution 6-3 flash A.O. Smith water heater 6-3 flash means Recycle limit exceeded: flame lost. See the verified model scope, safe checks, and official source. Search/display variants: 6-3 flash, 63flash caution 6-4 flash A.O. Smith water heater 6-4 flash means Recycle limit exceeded: flame out of sequence. Search/display variants: 6-4 flash, 64flash caution 7 flash A.O. Smith water heater 7 flash means Flammable Vapor Sensor (FVS) lockout. See the verified model scope, safe checks, and official source. Search/display variants: 7 flash, 7flash stop-use 8-1 flash A.O. Smith water heater 8-1 flash means Flammable Vapor Sensor fault detected. See the verified model scope, safe checks, and official source. Search/display variants: 8-1 flash, 81flash stop-use 8-2 flash A.O. Smith water heater 8-2 flash means Temperature sensor fault detected. See the verified model scope, safe checks, and official source. Search/display variants: 8-2 flash, 82flash caution 8-3 flash A.O. Smith water heater 8-3 flash means Electronics fault detected. See the verified model scope, safe checks, and official source. Search/display variants: 8-3 flash, 83flash caution 8-4 flash A.O. Smith water heater 8-4 flash means Valve fault detected. See the verified model scope, safe checks, and official source. Search/display variants: 8-4 flash, 84flash caution 031 The official ATIO 910 Service Handbook identifies 031 as incorrect dipswitch settings. Search/display variants: 031 caution 45-0 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies 45-0 as upper or lower temperature probe short condition. Search/display variants: 45-0, 450 caution 48-0 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies 48-0 as upper or lower temperature probe open condition. Search/display variants: 48-0, 480 caution 101 The official ATIO 910 Service Handbook identifies 101 as abnormal combustion. See the verified model scope, safe checks, and official source. Search/display variants: 101 caution 111 The official ATIO 910 Service Handbook identifies 111 as ignition failure. See the verified model scope, safe checks, and official source. Search/display variants: 111 caution 121 The official ATIO 910 Service Handbook identifies 121 as flame loss. See the verified model scope, safe checks, and official source. Search/display variants: 121 caution 311 The official ATIO 910 Service Handbook identifies 311 as output thermistor fault. Search/display variants: 311 caution 321 The official ATIO 910 Service Handbook identifies 321 as inlet thermistor fault. Search/display variants: 321 caution 331 The official ATIO 910 Service Handbook identifies 331 as mixing thermistor fault. Search/display variants: 331 caution 391 The official ATIO 910 Service Handbook identifies 391 as air-fuel ratio rod failure. Search/display variants: 391 caution 441 The official ATIO 910 Service Handbook identifies 441 as flow sensor fault. See the verified model scope, safe checks, and official source. Search/display variants: 441 caution 510 The official ATIO 910 Service Handbook identifies 510 as abnormal main gas valve. Search/display variants: 510 caution 551 The official ATIO 910 Service Handbook identifies 551 as abnormal solenoid gas valves. Search/display variants: 551 caution 611 The official ATIO 910 Service Handbook identifies 611 as abnormal fan motor. See the verified model scope, safe checks, and official source. Search/display variants: 611 caution 631 The official ATIO 910 Service Handbook identifies 631 as pump failure. See the verified model scope, safe checks, and official source. Search/display variants: 631 caution 651 The official ATIO 910 Service Handbook identifies 651 as abnormal flow adjustment valve. Search/display variants: 651 caution 661 The official ATIO 910 Service Handbook identifies 661 as bypass valve fault. See the verified model scope, safe checks, and official source. Search/display variants: 661 caution 681 The official ATIO 910 Service Handbook identifies 681 as external fan mode failure. Search/display variants: 681 caution 701 The official ATIO 910 Service Handbook identifies 701 as computer board fault. See the verified model scope, safe checks, and official source. Search/display variants: 701 caution 721 The official ATIO 910 Service Handbook identifies 721 as false flame detection. See the verified model scope, safe checks, and official source. Search/display variants: 721 stop-use 741 The official ATIO 910 Service Handbook identifies 741 as main remote control problem. Search/display variants: 741 caution 761 The official ATIO 910 Service Handbook identifies 761 as communication failure. See the verified model scope, safe checks, and official source. Search/display variants: 761 caution 991 The official ATIO 910 Service Handbook identifies 991 as abnormal combustion. See the verified model scope, safe checks, and official source. Search/display variants: 991 caution A6-501 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A6-501 as low gas pressure. Search/display variants: A6-501, A6501 caution A7-1201 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A7-1201 as blocked air intake. Search/display variants: A7-1201, A71201 caution A8-1201 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A8-1201 as blocked exhaust. Search/display variants: A8-1201, A81201 caution A9-17B 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. Search/display variants: A9-17B, A917B stop-use B2-70 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies B2-70 as ignition failure; flame not detected. Search/display variants: B2-70, B270 caution CC-B 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. Search/display variants: CC-B, CCB caution continuous flash 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… Search/display variants: continuous flash, continuousflash stop-use continuous on The official BTR 500 Service Handbook identifies continuous on as internal ignition-control-board failure. Search/display variants: continuous on, continuouson caution D6-8 The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies D6-8 as no water detected by the powered anode. Search/display variants: D6-8, D68 caution