Vaillant
Boiler Detection / Identification Failure
Vaillant smart thermostat shows 'No boiler connected' or similar message, but the boiler is installed and powered.
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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
eBUS not connected or reversed, Boiler not a compatible Vaillant eBUS model, Faulty boiler communication board, Incorrect controller type selected in setup
How to Fix / Troubleshooting
Safety: Isolate mains power to the boiler before accessing terminals.
- 1. Confirm compatibility: Check that the boiler is a Vaillant model supporting eBUS control. Older or non‑Vaillant boilers may require a different control method.
- 2. Inspect eBUS wiring: Verify that the two eBUS wires are correctly connected between boiler and thermostat, with no breaks or shorts.
- 3. Check controller setup: In the thermostat commissioning menu, ensure the correct boiler type and communication mode are selected.
- 4. Test with short cable: Temporarily connect the thermostat directly at the boiler with a short cable to rule out wiring issues.
- 5. Technician diagnosis: If the boiler still cannot be detected, a Vaillant engineer should test the boiler’s eBUS board and replace if necessary.
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Repair Difficulty
Hard
4/5
Required Part
Boiler eBUS communication board
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