303
Ariston
External Control / Bus Communication Fault
Boiler displays 303, external controls (room thermostat, timer) not recognised
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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
Incorrect wiring of room thermostat, Faulty Ariston bus connection, Damaged low-voltage cable, Incompatible control device
How to Fix / Troubleshooting
Safety: Isolate power before working on control wiring.
- Check thermostat wiring: Verify that the room thermostat or Ariston Cube/Net is wired to the correct terminals as per the installation manual.
- Inspect cable: Look for damage or joints in the low-voltage cable between boiler and control. Replace if suspect.
- Test with link: Temporarily fit a link wire across the boiler's room stat terminals (if allowed by the manual). If the boiler then responds, the external control or its wiring is faulty.
- Compatibility: Ensure the control is compatible with your Ariston boiler model and bus protocol.
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Repair Difficulty
Medium
3/5
Required Part
Room Thermostat / Bus Interface
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