E08
Delta Dore
Bus Communication Failure with Boiler Interface
E08 displayed and thermostat cannot detect the boiler interface module; heating remains off.
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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
Disconnected Delta Dore boiler interface bus cable, Reversed polarity on bus terminals, Boiler interface module not powered, Incompatible boiler protocol configuration
How to Fix / Troubleshooting
Safety first: Turn off power to the boiler and boiler interface module before touching any wiring.
- Check bus wiring: Locate the Delta Dore boiler interface (e.g. OpenTherm or proprietary bus module). Verify that the two bus wires are firmly connected to the thermostat or receiver and to the boiler terminals as per the wiring diagram.
- Polarity and pairing: Some bus systems are polarity-sensitive. Ensure the + and – (or A/B) terminals are correctly matched between boiler and interface.
- Power to interface: Confirm that the boiler interface module has power (LEDs lit). If not, check its supply fuse or boiler internal fuse.
- Protocol configuration: In the thermostat installation menu, ensure the correct boiler type/protocol is selected (e.g. OpenTherm vs on/off). An incorrect setting can trigger E08.
If wiring and configuration are correct and E08 persists, the boiler interface module may be defective and should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Delta Dore Boiler Interface Module
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