EcoSmart ECO 24 Error Codes — What It Means
EcoSmart ECO 24 error codes indicate specific faults in the tankless water heater’s temperature sensing, flow control, or power supply. E1 signals an inlet thermistor problem, E2 points to an outlet thermistor issue, and E3 means both thermistors or the temperature-sensing circuit have failed. E4 is a high-temperature fault (inlet water is already too hot for safe operation), E5 is a high-flow fault (water is flowing too fast for the heater to reach setpoint), and S103 indicates a low-voltage or supply-power problem.
The ECO 24 shares a common troubleshooting platform with the ECO 8, 11, 18, 27, and 36 models. The unit requires an activation flow rate of approximately 0.3 GPM to turn on and depends on correct 240 V wiring, proper breaker sizing, and adequate wire gauge to operate reliably. Many error codes can be cleared or diagnosed using the heater’s built-in calibration mode, but persistent faults usually trace back to failed sensors, incorrect installation, or supply-side conditions outside the heater’s operating envelope.
Common Causes
- Failed or disconnected thermistor E1, E2, or E3 codes appear when the inlet or outlet temperature sensor has failed internally or its wire connector has come loose from vibration or corrosion.
- Inlet water temperature too high E4 triggers when incoming water exceeds the heater’s safe operating range, common in recirculation loops or when feed water is pre-heated by solar or another source.
- Flow rate exceeds heating capacity E5 occurs when water flows too fast for the ECO 24 to raise temperature to setpoint, especially with very cold inlet water or a high temperature dial setting.
- Low or unstable supply voltage S103 and intermittent operation result from supply voltage below 240 V, undersized wire, loose breaker connections, or a faulty breaker that cannot deliver rated amperage.
- Incorrect wiring or crossed hot/neutral Reversed or crossed wires prevent proper element control and can cause nuisance fault codes or failure to heat even when the display powers on.
- Water flow too low to activate If flow is below approximately 0.3 GPM the heater will not turn on, and if flow fluctuates around that threshold the unit may cycle or throw intermittent faults.
Step-by-Step Fix {#fix}
- Verify power and wiring by confirming all breakers are on, wire gauge matches the manufacturer table for your model, breakers are correctly sized, and ground is intact.
- Check supply voltage at the heater’s input terminals with a multimeter under no-load and under-load conditions to confirm stable 240 V (or at least 208 V minimum) and rule out S103 low-voltage faults.
- Confirm flow rate and pressure by measuring flow at the fixture and checking that incoming pressure is adequate and that flow is above the 0.3 GPM activation threshold but not so high that E5 appears.
- Run the calibration sequence for E1, E2, or E3 thermistor codes by turning on hot water so the error displays, then press and hold the round temperature-adjust knob for 3 to 5 seconds until the display changes to CE1 or CE2, and keep water running for 2 to 3 minutes to see if hot water returns and the fault clears.
- Install a flow restrictor or regulator if E5 persists, reducing flow so the heater can meet the set temperature without exceeding its kW capacity at the given inlet condition.
- Inspect and replace thermistors if calibration does not clear E1, E2, or E3 by disconnecting power, removing the cover, unplugging the sensor connector, and installing a new thermistor matched to your model.
- Contact EcoSmart support if the error returns after calibration and part replacement, or if E4 or other codes persist after verifying installation parameters, since some faults require board-level diagnosis or firmware intervention.
Parts Often Needed
| Part | Notes |
|---|---|
| EcoSmart inlet thermistor | Amazon | Confirm part number for ECO 24 before ordering. |
| EcoSmart outlet thermistor | Amazon | Verify compatibility with your serial-number range. |
| Flow restrictor or EcoSmart flow regulator | Amazon | Helps prevent E5 high-flow faults on high-pressure supplies. |
When to Call a Pro
Call a licensed electrician or EcoSmart-trained technician if you measure low or fluctuating voltage and cannot identify the cause, if wiring or breaker replacement is needed, or if thermistor replacement and calibration do not resolve E1, E2, or E3 codes. Professional help is also recommended for E4 faults that do not match actual inlet temperature (indicating a control-board issue) and for any situation where the heater trips breakers repeatedly or shows signs of arcing or overheating at terminals. EcoSmart provides model-specific troubleshooting guides and direct support for the ECO 24 family, so reach out to the manufacturer if DIY steps do not restore normal operation.