E3
Rheem
Outlet Thermistor (Hot Water Temperature Sensor) Fault
Rheem tankless water heater shows E3 and shuts down during operation
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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
Failed outlet thermistor, Loose or corroded thermistor connector, Damaged thermistor wiring harness, Overheated outlet causing sensor damage
How to Fix / Troubleshooting
Safety first: Turn OFF power and gas. Let the heater cool.
- Locate outlet thermistor: Remove the front cover. Find the thermistor on the hot water outlet pipe or manifold (often labeled TH2 or Outlet).
- Check connection: Verify the thermistor plug is firmly connected to the main control board and free of corrosion.
- Visual inspection: Look for discoloration, melted plastic, or scale buildup around the sensor. Clean light scale carefully.
- Test sensor: Disconnect the thermistor and measure resistance with a multimeter. Compare to Rheem's temperature/resistance chart. Replace if open, shorted, or out of spec.
- Install replacement: Shut off water and relieve pressure. Unscrew the old sensor, install the new outlet thermistor with the supplied O-ring or sealant, reconnect wiring, and restore power.
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Repair Difficulty
Medium
3/5
Required Part
Outlet Thermistor
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