Saunier Duval Control Signal Not Reaching Boiler

Thermostat calls for heat but boiler does not start (no error code on thermostat or boiler)

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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

Loose eBus/OTBus connection at boiler, Thermostat configured for wrong control mode (on/off vs bus), Faulty boiler room thermostat input terminals, Broken low-voltage cable between thermostat and boiler

How to Fix / Troubleshooting

Safety: Isolate mains power to the boiler before opening its casing or touching any internal wiring.

  • Check demand icon: Confirm the thermostat actually shows a heating demand (flame or radiator icon). If not, increase the setpoint above room temperature.
  • Verify wiring: At the boiler, check that the thermostat cable is connected to the correct terminals (eBus/OTBus or room thermostat contacts) as per Saunier Duval wiring diagram.
  • Continuity test: With power off, test the cable between thermostat and boiler for continuity and repair/replace if open.
  • Mode configuration: In the thermostat installer menu, ensure the control type matches the boiler connection (bus vs on/off).

If wiring and configuration are correct but the boiler still does not respond, the boiler control board or thermostat output may be faulty; contact a qualified technician.

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Repair Difficulty

Hard 4/5

Required Part

Saunier Duval eBus/OTBus Cable or Room Thermostat Cable
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