System reports an overheat or safety shutdown; boiler stops even though thermostat is calling for heat.

Danger: Overheating boilers can be hazardous. If you smell burning or see signs of overheating, switch off power and contact a professional immediately.

• Check boiler display: Look for error codes or overheat warnings on the boiler itself and follow the manufacturer’s reset procedure.
• Verify circulation: Ensure radiators are warm and that the circulation pump is running when the boiler fires. If radiators stay cold, there may be a hydraulic issue unrelated to the thermostat.
• Observe thermostat behavior: If the thermostat is constantly calling for heat (flame icon always on) even when room is warm, the Relay’s contact may be stuck closed. Power‑cycle the Relay and see if behavior changes.
• Temporarily disconnect thermostat (advanced): With power OFF, remove one thermostat control wire at the boiler. Restore power: if the boiler still overheats or locks out, the issue is in the boiler, not the Netatmo system.

Persistent overheat or lockout conditions require a qualified boiler technician. If the Netatmo Relay contact is confirmed stuck closed, replace the Relay.