A61
Bosch Communication Error with Control Interface

Furnace displays A61; unit may not respond to thermostat or internal controls

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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 or damaged bus cable between main PCB and user interface, Incorrect polarity on low-voltage connections, Faulty control panel, Main control board failure

How to Fix / Troubleshooting

Safety: Isolate mains power before removing any covers.

  • Check low-voltage wiring: Open the control compartment and inspect the communication cable between the main control board and the Bosch room controller or thermostat interface. Ensure connectors are fully seated and wires are not reversed.
  • Look for damage: Replace any cable that shows cuts, crushed insulation, or burn marks.
  • Power cycle: Turn power off for at least 30 seconds, then restore. Sometimes A61 clears after a full reset.

If the error persists with known-good wiring, either the user interface module or the main PCB is defective. A Bosch service technician should perform module substitution and configuration.

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Repair Difficulty

Medium 3/5

Required Part

Main Control Board
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