E12
EcoSmart
Temperature Sensor Calibration / Mismatch Fault
Unit displays E12; may coincide with very hot outlet temperatures or erratic readings.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Non-OEM thermistor installed, Mixed sensor types on inlet and outlet, Control board firmware not matched to sensor set, Damaged sensor harness causing intermittent readings
How to Fix / Troubleshooting
Safety: Turn OFF power and close water supply before opening the unit.
- Confirm sensor types: Verify that both inlet and outlet temperature sensors are genuine EcoSmart parts specified for your model. Mismatched sensors can cause calibration errors.
- Inspect harness: Check the combined sensor harness for splices, damage, or aftermarket modifications. Replace with the correct harness if needed.
- Reseat connectors: Disconnect and reconnect both inlet and outlet thermistor plugs at the control board.
- Firmware check: If the control board was recently replaced, confirm with EcoSmart that the board firmware matches your heater model and sensor set.
- Test operation: Restore power and run hot water at a moderate setting. If E12 persists, replace both temperature sensors as a matched pair.
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Repair Difficulty
Medium
3/5
Required Part
Inlet and Outlet Temperature Sensors (Matched Set)
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