EcoSmart ECO 26 Error Codes — What It Means
EcoSmart ECO 26 electric tankless water heaters display alphanumeric fault codes when the control board detects a problem. The most common codes are E1 (inlet thermistor fault), E2 (outlet thermistor fault), E3 (both thermistors faulted), and E5 (excessive flow or insufficient temperature rise). E1, E2, and E3 indicate the control board cannot read temperature correctly from one or both sensor probes, which prevents safe operation. E5 means water is flowing through the heater faster than the heating elements can raise the temperature to your setpoint, triggering a temperature-rise limit condition.
These codes protect the heater from unsafe operation and component damage. Thermistor codes usually point to a failed sensor, corroded connector, or bad control board. The E5 flow fault typically means you are asking the heater to deliver more hot water than it can produce given the incoming cold-water temperature and available electrical power. Identifying the exact code on your display is the first step to accurate diagnosis and repair.
Common Causes
- Failed thermistor sensor The inlet or outlet temperature probe has failed internally or the resistance is out of specification, causing E1, E2, or E3 codes.
- Corroded or loose wiring connections Thermistor connectors or terminals have corrosion, water intrusion, or poor contact, preventing the control board from reading temperature.
- Excessive flow rate through the heater Water demand exceeds the heater’s capacity at the current inlet temperature, triggering E5 because the unit cannot achieve the required temperature rise.
- Inlet water temperature too cold Very cold incoming water reduces the effective capacity of the heating elements, making it impossible to meet setpoint at normal flow rates and causing E5.
- Missing or incorrect flow restrictor The application requires a flow restrictor to limit gallons per minute, but it is not installed or sized correctly, allowing flow to exceed heater capacity.
- Defective control board The main control board has failed and cannot accurately read thermistor inputs or manage element firing, resulting in false or persistent fault codes.
Step-by-Step Fix {#fix}
- Power off the unit at the circuit breaker and verify zero voltage at the heater terminals with a multimeter before opening the cover or touching any components.
- Note the exact error code displayed on the front panel and refer to your model’s documentation to confirm the fault category (thermistor or flow related).
- Inspect thermistor connectors inside the heater for corrosion, moisture, or loose pins if you see E1, E2, or E3, then disconnect each thermistor and measure resistance across the probe leads with the multimeter set to ohms.
- Replace the faulty thermistor if resistance is infinite, zero, or far outside the expected range for room temperature (consult your model’s specification table for target values).
- Check flow rate at a fixture if you see E5 by timing how long it takes to fill a one-gallon container, then calculate gallons per minute and compare to the heater’s rated capacity at your inlet temperature.
- Reduce flow by partially closing the inlet shutoff valve or outlet service valve, or install a flow restrictor at the fixture if the calculated demand exceeds heater capacity.
- Restore power and test by opening a hot-water tap and observing the display to confirm the error code clears and the heater reaches setpoint temperature within a few seconds of flow starting.
Parts Often Needed
| Part | Notes |
|---|---|
| Inlet or outlet thermistor sensor | Amazon | Order by exact ECO 26 model number to match probe thread and connector type. |
| Flow restrictor insert | Amazon | Match gallons-per-minute rating to your heater capacity and fixture requirements. |
| Control board assembly | Amazon | Required if thermistor inputs read correctly but faults persist after sensor replacement. |
When to Call a Pro
Call a licensed electrician or plumber if you are not comfortable working with 240-volt circuits, if multimeter diagnostics show normal thermistor resistance but codes persist, or if you have replaced sensors and adjusted flow but the heater still faults. Persistent E1, E2, or E3 codes after thermistor replacement usually mean control-board failure, which requires de-energizing high-voltage wiring and matching the exact board revision to your serial number. A professional can also verify that your electrical service delivers the correct voltage and amperage to all heating elements, since low voltage or a tripped breaker on one pole can mimic flow or temperature faults.