ecobee thermostats require a constant 24VAC power supply from your HVAC system to operate. If your ecobee thermostat is frequently rebooting, your HVAC system may be cutting power the thermostat.
The most common causes of your HVAC system cutting power to your thermostat are:
1. The furnace is overheating: All furnaces contain a safety mechanism called a high-limit temperature sensor. If your furnace overheats, this sensor will trip, causing the furnace to cut power to your thermostat. The furnace may run the fan to help cool off the furnace, or may not carry out any function until the system is reset or the furnace cools down sufficiently. For info on how to troubleshoot an overheating furnace, visit the following article: My furnace won’t turn on! How can I troubleshoot?
2. A tripped float switch: Your furnace should contain a float switch to prevent flooding if there is a build-up of water from condensation. If water from condensation is not being drained quickly enough it can trigger the float switch, which will then cut power to your thermostat. For info on how to troubleshoot a tripped float switch, visit the following article: My air conditioning won’t turn on! How can I troubleshoot?