A.O. Smith Error Code E1: Thermistor Failure
Warning: Your A.O. Smith water heater has detected a problem with one of its temperature sensors and has shut down to prevent potential overheating or other issues. You will not have hot water until this is resolved.
How to Fix A.O. Smith Code E1
- Step 1: Check the water heater's display for any other error codes. Note them down, as they may provide additional clues.
- Step 2: Reset the water heater by turning off the power at the breaker for 30 seconds, then turning it back on. This may clear a temporary error.
- Step 3: If the E1 error persists after resetting, contact a qualified HVAC technician to diagnose and repair the issue.
How to Reset A.O. Smith Code E1
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
What does E1 mean?
The E1 error code on your A.O. Smith tankless water heater indicates a problem with one of its thermistors. Thermistors are temperature-sensitive resistors that send temperature readings to the unit's control board. The control board uses these readings to regulate the burner and ensure safe and efficient operation. An E1 error specifically points to a failure or out-of-range reading from either the inlet or outlet thermistor. This could be due to a faulty sensor, wiring issues, or a problem with the control board itself. Because the unit cannot accurately monitor water temperature, it shuts down to prevent potential overheating or damage.
Affected Models
Replacement Parts
| Part | OEM Number | Est. Cost |
|---|---|---|
| Inlet Thermistor | 9005329005 | — |
| Outlet Thermistor | 9005329005 | — |
| Control Board | — | — |
Related Codes on Same Models
| Code | Description | Severity |
|---|---|---|
| E2 | Dry Fire Protection | Warning |
| E3 | Sensor Fault | Warning |
| E4 | High Temperature Cutoff | Critical |
| E5 | Communication Error | Warning |
| E06 | Flammable Vapor Detection | Critical |
| ECO | Emergency Cutoff | Critical |
| LOC | Controls Locked | Warning |
| UPR | Upper Element Fault | Warning |
| LWR | Lower Element Fault | Warning |