The ecobee thermostat has a built in freeze protection feature that will automatically engage the furnace/boiler heat if:
- the thermostat's internal temperature sensor drops below 41F/5C
- the thermostat is in Heat mode indicated by a flame icon
When this feature kicks in:
- the ecobee will set the thermostat itself as the only participating sensor
- the ecobee will continue to ignore other room sensor temperatures until the temperature rises above 41F/5C
This feature is enabled by default and cannot be disabled.