We changed the batteries. The yellow light, but not the green energy saver light is on. It says it is 68 degrees and it is set at 72. The fan is only going on when I move it to fan on instead of auto. We had the fan fixed this summer, but the technician didn't check out the furnace. I am trying to figure out if it is the furnace or the thermostat.

Make sure the power is turned on to the furnace (circuit breaker and furnace disconnect switch if equiped).