Unit powers on but does not heat water; display shows E1 shortly after opening a hot water tap.

Safety first: Turn OFF the circuit breaker supplying the EcoSmart water heater and verify power is off with a non-contact voltage tester before removing the cover. Close the cold water supply valve.

• Access the sensors: Remove the front cover of the EcoSmart unit (typically several Phillips or Torx screws). Locate the inlet temperature sensor (thermistor) on the cold water inlet pipe/manifold.
• Inspect connections: Check the thermistor plug where it connects to the main control board. Reseat the connector firmly. Look for corrosion, discoloration, or broken locking tabs.
• Check wiring: Follow the sensor harness from the inlet thermistor to the control board. Look for pinched, cut, or burned insulation. Repair or replace damaged wiring.
• Test the thermistor (if you have a multimeter): Disconnect the sensor and measure resistance across its leads. Compare to EcoSmart’s temperature/resistance chart (resistance should change smoothly with temperature; an open or shorted reading indicates failure).
• Reset and test: Restore water supply, reassemble the cover, turn the breaker ON, then open a hot tap. If E1 persists after reseating and inspection, the inlet thermistor is likely defective and should be replaced.
• When to call a pro: If a new inlet sensor does not clear E1, the control board’s sensor input circuit may be faulty and should be diagnosed/replaced by a qualified technician.