H4
Tosot
Indoor–Outdoor Mismatch / EEPROM Compatibility Error
Indoor unit displays H4, unit may not start or may stop mid-cycle
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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
Indoor and outdoor units from different capacity series, Replacement PCB with wrong software version, Incorrect configuration settings on PCB
How to Fix / Troubleshooting
Safety first: Turn off power to the system.
- Verify model compatibility: Confirm that the indoor and outdoor Tosot models are approved to work together.
- Check PCB part numbers: Ensure any replaced boards match the original part numbers or approved substitutes.
- Reconfigure if applicable: Some boards allow capacity or model selection via DIP switches; set them correctly.
- If H4 persists: Replace the mismatched PCB or unit with the correct model.
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Repair Difficulty
Hard
4/5
Required Part
Indoor Main Control Board
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