2021 Lennox Warranty call. 10/10/10 Checked system and found blown fuse on zone board. Checked all low voltage and could not find any indication of what caused fuse to blow. Checked damper opening and closing. Checked all wiring. Replaced fuse with spare on zone board. Started system and let run. System ran for 30 minutes. Pressures are good. Checked amp draw. Customer is unaware if any outages have occurred recently. Unit is working at this time.