E15
State
Power Supply / Low Voltage Error
State tankless water heater displays E15; unit may not start or may shut down unexpectedly.
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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
Incorrect line voltage, Loose power connections, Tripped internal fuse, Faulty transformer on control board
How to Fix / Troubleshooting
Safety: Turn off power at the breaker before opening electrical compartments.
- Verify supply: Confirm the heater is connected to the correct voltage (typically 120 VAC) and that the breaker is properly sized.
- Inspect wiring: Check the line and neutral connections at the junction box and control board for tightness and signs of overheating.
- Internal fuse: Some State boards have a replaceable fuse. Test and replace only with the same type and rating if blown. Investigate cause of failure.
- Transformer/board: If correct voltage is present at the input but the board does not power up properly, the internal power supply section may have failed and the board should be replaced.
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Repair Difficulty
Medium
3/5
Required Part
Main Control Board (PCB)
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