Have HVAC Questions? Ask an HVAC Expert for Answers
Hi I'm Brian and I'm here to help!
The only battery the Lennox ComfortSense series thermostat has is a tiny lithium battery to keep the clock in time. All important data in the thermostat is held in non-volatile memory. Unfortunately the lithium battery is not user replaceable and should last for a minimum of 10 years (more likely 15).
If your thermostat is losing its time when the power fails, unfortunately the battery has probably failed. Your options are to either replace the thermostat or reset the time after a power fail. Fortunately all schedules and run times should be saved. I'm sorry to be the bearer of not-so-good-news.