E10
Bosch
Digital BUS Communication Failure
Thermostat shows E10 and indicates communication loss with Bosch boiler or heat pump over BUS/eBUS/EMS interface.
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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 reversed polarity on Bosch BUS/eBUS wiring, BUS cable disconnected at boiler control module, Incorrect BUS address or protocol configuration, Faulty BUS interface on thermostat or boiler control board
How to Fix / Troubleshooting
Safety: Turn off power to the boiler/heat pump at the main switch or breaker before touching BUS wiring.
- Check BUS wiring: At the thermostat, verify the BUS+ and BUS− (or B1/B2, EMS terminals) are correctly landed and not swapped. Repeat at the boiler control module.
- Inspect cable: Follow the BUS cable where accessible. Look for cuts, pinches, or junctions that may have come loose.
- Verify configuration: In the installer menu, confirm the thermostat is set to the correct communication mode (e.g., Bosch EMS/eBUS) and that any addressing or device ID settings match the boiler’s requirements.
- Power cycle system: Turn off power to the boiler and thermostat for 1–2 minutes, then restore power to reset the BUS network.
- If E10 persists: Either the thermostat BUS interface or the boiler’s BUS module may be defective. Professional diagnostics with Bosch service tools is recommended.
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Repair Difficulty
Hard
4/5
Required Part
Bosch BUS/eBUS Communication Cable or Boiler BUS Module
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