Thermostat displays E9, reporting an internal hardware fault.

Safety: No high-voltage work is required at the thermostat. Do not attempt to open or repair the internal electronics.

• Step 1 – Power cycle from the breaker: Turn off the furnace/air handler breaker for 2–3 minutes, then restore power. Allow the Ecobee to fully reboot.
• Step 2 – Remove and reseat thermostat: Gently pull the Ecobee off its backplate, wait 30 seconds, then snap it back on to ensure good pin contact.
• Step 3 – Check for overheating: Make sure the thermostat is not installed above a heat source or in direct sunlight. Overheating can trigger hardware faults.
• Step 4 – Factory reset (last resort): Go to Menu > Settings > Reset > Reset All. This will erase all settings and require reconfiguration. Only do this after backing up any needed settings.
• Step 5 – Replace thermostat: If E9 persists after reset and power cycling, the internal board is likely defective. Replace the Ecobee thermostat.