A.O. Smith Error Code ECO: Emergency Cutoff
How to Fix A.O. Smith Code ECO
- Step 1: Immediately stop using hot water to prevent further temperature increase.
- Step 2: Carefully check the area around the water heater for any signs of leaks or unusual smells (like burning plastic). If you notice anything, leave the area immediately.
- Step 3: Contact a qualified HVAC technician or plumber to inspect the water heater and diagnose the problem. Do not attempt to reset the high limit switch yourself.
How to Reset A.O. Smith Code ECO
- 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.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does A.O. Smith Error Code ECO Mean?
The A.O. Smith water heater's 'ECO' or Emergency Cutoff code signifies that the high limit switch has tripped. This switch is a crucial safety device designed to shut down the water heater if the water temperature exceeds a pre-set limit, typically around 190-200°F. When this happens, the heater stops working to prevent dangerous conditions like scalding hot water or, in extreme cases, a tank rupture due to excessive pressure and temperature. Ignoring this warning can be very dangerous. This error is not something to take lightly. It means the system detected a problem that could cause harm. The most common reasons for this are overheating due to a faulty thermostat, a malfunctioning heating element that won't shut off, or a blockage in the tank that prevents proper water circulation. Because this is a safety issue, it's important to get it checked out by a qualified technician.
Common Causes
- Faulty thermostat causing overheating
- Failed heating element continuously heating the water
- Sediment buildup in the tank restricting water flow and causing localized overheating
- Defective high limit switch tripping prematurely
- Incorrectly wired or installed heating element
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| ECO code is displayed | Measure voltage at the heating element terminals with the thermostat calling for heat. | 0 VAC if the high limit switch is tripped. Line voltage if the high limit switch is closed. |
| High limit switch is tripped (no voltage at heating element) | Check continuity across the high limit switch after manually resetting it (if possible). | Continuity when reset. No continuity if the switch is faulty and remains open. |
| High limit switch trips immediately after resetting | Measure the resistance of each heating element. | Should be within the specified range (typically 9-13 ohms for a 4500W element at 240V). Significantly lower resistance indicates a shorted element. |
| Heating element resistance is normal, and high limit switch trips | Drain the tank and inspect for excessive sediment buildup. | Minimal sediment. Excessive sediment indicates a need for flushing and potential cause of overheating. |
Applicable A.O. Smith Models
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| High Limit Switch | — | — | — |
| Heating Element | — | — | — |
| Thermostat | — | — | — |
Related Codes on Same Models
Other codes that affect the same A.O. Smith model families as ECO.
| Code | Description | Severity |
|---|---|---|
| E06 | Flammable Vapor Detection | Critical |
| E1 | Thermistor Failure | Warning |
| E2 | Dry Fire Protection | Warning |
| E3 | Sensor Fault | Warning |
| E4 | High Temperature Cutoff | Critical |
| E5 | Communication Error | Warning |
| LOC | Controls Locked | Warning |
| LWR | Lower Element Fault | Warning |
| UPR | Upper Element Fault | Warning |