C1
Bosch
Communication Error Between Control Boards
Bosch water heater displays C1; unit may lock out or require reset
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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
Loose communication harness between main PCB and display board, Damaged low-voltage wiring, Faulty user interface board, Defective main control board
How to Fix / Troubleshooting
Safety first: Turn OFF power at the breaker before accessing internal electronics.
- Inspect communication cable: Remove the front cover and locate the cable between the main control board and the display or user interface board. Ensure both ends are fully seated.
- Check for damage: Look for pinched, cut, or burned wires along the harness route. Replace the harness if damaged.
- Reseat connectors: Disconnect and reconnect the harness at both boards to clean contact surfaces.
- Power cycle: Restore power and see if the error clears. If C1 persists, either the display board or main PCB may be faulty.
- Professional diagnosis: Board-level diagnosis and replacement should be performed by a qualified technician to avoid misdiagnosis and ensure safe operation.
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Repair Difficulty
Hard
4/5
Required Part
User Interface / Display Board
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