F12
Saunier Duval
Room Thermostat / Communication Fault
Boiler displays F12 and does not respond to thermostat commands
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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 circuit in room thermostat wiring, Faulty eBUS or OT communication with Saunier Duval controller, Incorrect wiring at boiler terminals, Defective room thermostat
How to Fix / Troubleshooting
Safety first: Isolate power before accessing the wiring terminals.
Steps to check:
- Verify that the room thermostat or controller has power (batteries or mains).
- Check the wiring between the thermostat and the boiler's low-voltage control terminals (e.g., eBUS, OT, or on/off contacts).
- Ensure correct polarity and that no wires are loose or shorted.
- If using a Saunier Duval proprietary controller, power-cycle both the boiler and controller to re-establish communication.
- If F12 persists, test with a simple link (for on/off controls) or substitute controller to confirm if the thermostat is faulty.
Warning: Low-voltage control circuits are still part of the boiler safety system. If unsure, consult a qualified technician.
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Repair Difficulty
Medium
3/5
Required Part
Room Thermostat / eBUS Controller
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