A90
Buderus
BUS Communication Fault (e.g., Logamatic, cascade control)
Boiler displays A90; communication with external control or cascade manager fails
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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
Broken BUS wiring between boiler and control, Incorrect BUS addressing, Faulty Logamatic module, Electrical interference on BUS line
How to Fix / Troubleshooting
Safety: Turn off power to all connected modules before altering BUS wiring.
- 1. Identify BUS topology: Determine how the Buderus boiler is connected to Logamatic controls or other boilers (cascade). Note all BUS modules.
- 2. Check wiring: Inspect the BUS cable for damage, loose terminals, or incorrect polarity. Ensure shielded cable is used where specified.
- 3. Addressing and configuration: Verify that each module has a unique address and that the boiler is correctly configured for BUS operation in the service menu.
- 4. Isolate fault: Disconnect BUS devices one by one to see when A90 clears. This can identify a faulty module.
- 5. Replace faulty module: If a specific Logamatic module or interface is causing the fault, replace it with the correct Buderus part.
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Repair Difficulty
Hard
4/5
Required Part
BUS Interface / Logamatic Control Module
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