Thermostat shows E260 indicating internal memory or firmware error; may reboot repeatedly or lose settings.

Safety warning: Turn off power to the thermostat before removing it from the wall if physical replacement is needed.

• 1. Power cycle:
  • Turn off the HVAC breaker for 5 minutes, then restore power.
  • Observe if the thermostat boots normally.
• 2. Factory reset (if accessible):
  • From the thermostat menu, perform a factory reset following Lennox instructions.
  • Reconfigure equipment settings afterward.
• 3. Firmware reload:
  • If Lennox provides a firmware recovery method (USB or service tool), follow their procedure to reload firmware.
• 4. Replace thermostat if unresolved:
  • Persistent E260 usually indicates a failed thermostat main board.
  • Install a new Lennox smart thermostat compatible with your system.