E1
Tosot
Indoor–Outdoor Communication Failure
Indoor unit stops and displays E1, outdoor unit does not respond
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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
Open or shorted communication cable between indoor and outdoor units, Reversed polarity on power/communication terminals, Failed indoor main PCB communication circuit, Failed outdoor main PCB communication circuit
How to Fix / Troubleshooting
Safety first: Turn off power at the outdoor disconnect and indoor breaker before touching wiring.
- Verify wiring connections: Remove the terminal covers on both indoor and outdoor units. Confirm that terminals 1–2–3 (or L–N–S depending on model) match exactly between units and that screws are tight.
- Check for damaged cable: Inspect the interconnecting cable for cuts, rodent damage, or crushed sections. Replace the cable if any conductor is exposed or insulation is damaged.
- Polarity check: Ensure live (L), neutral (N), and signal (S) are not swapped. Incorrect polarity is a common cause of E1 on Tosot mini-splits.
- Power cycle: After correcting wiring, restore power and wait 5–10 minutes. Try starting the unit again.
- If E1 remains: One of the PCBs (indoor or outdoor) may have a failed communication circuit. A technician should test DC bus voltage and communication signal; replace the faulty PCB.
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Repair Difficulty
Hard
4/5
Required Part
Interconnecting Communication Cable
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