EcoSmart ECO 20 Error Codes — What It Means
The ECO 20 is a model designation, not an error code. The actual fault codes are E1 through E5 and S103. E1 signals an inlet thermistor problem, E2 indicates an outlet thermistor fault, and E3 means both sensors or the broader temperature-sensing circuit has failed. E4 warns that incoming water temperature is too high for safe operation, E5 appears when flow rate exceeds the heater’s capacity to raise temperature, and S103 flags a low-voltage condition at the unit.
These codes point to temperature sensor failures, flow mismatches, voltage deficiencies, or demand that outstrips the heater’s ability. The manufacturer troubleshooting guide ties most problems to incorrect wiring, flow rates below the 0.5 GPM activation threshold, flow rates too high for the unit’s kW rating, supply voltage below design (240 V), and mixing of cold water at fixtures or through anti-scald valves.
Common Causes
- Incorrect or crossed wiring Breakers off, reversed line connections, or improper wire gauge prevent the heater from receiving stable power.
- Flow rate too low to activate The ECO troubleshooting guide lists an activation threshold of approximately 0.5 GPM, and flow below that will not trigger heating.
- Flow rate too high for heating capacity Demand exceeds the unit’s kilowatt rating, so outlet water cannot reach the set temperature and triggers E5.
- Supply voltage below design value Elements are designed for 240 volts, and lower voltage reduces heating performance or triggers S103 faults.
- Cold water mixing at fixtures or valves Anti-scald valves, tempering valves, or user adjustment at the tap blend cold water and reduce delivered hot-water temperature.
- Failed inlet or outlet thermistor Temperature sensors report faulty readings or open circuits, generating E1, E2, or E3 codes.
Step-by-Step Fix {#fix}
- Verify power and wiring first. Confirm all breakers are on, measure incoming voltage at the heater terminals (should meet 240 V design or at least 208 V minimum), and inspect connections for crossed or loose wires, especially if the installation is new.
- Measure flow rate at the heater inlet. Open a single fixture fully and confirm flow meets or exceeds the 0.5 GPM activation threshold listed in the ECO troubleshooting guide.
- Check demand versus capacity. If water is warm but not hot enough, reduce flow at the faucet or adjust the inlet shutoff valve to lower GPM, or install an EcoSmart flow regulator matched to your model’s kilowatt rating.
- Inspect fixtures for cold-water mixing. Look for anti-scald devices, tempering valves, or user blending at the tap that dilutes hot water, and adjust or remove them if appropriate.
- For thermistor codes E1, E2, or E3, inspect the temperature sensors. Check wiring to the inlet and outlet sensors for damage or loose terminals, and if the code persists after confirming flow and power, replace the faulty thermistor or contact technical support for internal diagnostics.
- For E4 high-temperature faults, confirm inlet water temperature. If source water exceeds safe limits, consult the manual’s temperature-rise table and adjust fixture flow to prevent overheating.
- Reset the heater only after correcting the root cause. The manufacturer emphasizes fixing flow, wiring, voltage, or capacity mismatches rather than relying on a temporary reset to clear codes.
Parts Often Needed
| Part | Notes |
|---|---|
| EcoSmart inlet thermistor | Amazon | Order the sensor assembly specific to your ECO model; verify part number in the unit’s technical documentation. |
| EcoSmart outlet thermistor | Amazon | Match the replacement sensor to your heater’s model and serial number to make sure correct resistance and connector type. |
| EcoSmart flow regulator | Amazon | Select the regulator sized for your model’s kilowatt rating to prevent high-flow E5 faults. |
When to Call a Pro
Call a licensed electrician if you measure low voltage at the panel, suspect undersized branch wiring, or see evidence of overheating at terminals. Contact a plumber or EcoSmart technical support if thermistor codes persist after you have confirmed proper flow and power, if you are unfamiliar with disassembling the heater cabinet to access internal sensors, or if E4 and E5 codes continue despite adjusting flow and fixture mixing. Professional diagnosis is also warranted when multiple codes appear simultaneously or when you cannot achieve the temperature rise shown in your model’s capacity table despite correct installation practices.