E18
State
Freeze Protection / Low Ambient Temperature Error
State tankless water heater shows E18; unit may lock out during very cold inlet conditions.
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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 freeze protection sensor, Inoperative freeze protection heaters, Unit installed in unconditioned space below rating
How to Fix / Troubleshooting
Safety: Turn off power before testing electrical heaters.
- Check location: Verify the heater is installed within the ambient temperature range specified by State. Provide additional insulation or relocation if necessary.
- Inspect freeze heaters: On models with built-in freeze protection, locate the pipe and base heaters. Check for continuity with a multimeter. Replace any open heaters.
- Freeze sensor: Test the ambient/freeze sensor resistance and compare to spec. Replace if out of range.
- Power supply: Ensure the unit has continuous power during cold weather so freeze protection can operate.
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Repair Difficulty
Hard
4/5
Required Part
Freeze Protection Heater Kit
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