Thermostat is blank. Furnace won't work. Findings: (1) Opened the system to find the low voltage fuse had popped. (2) Took off all the thermostat wiring and tried restarting the system with a new fuse. (3) System ran through heating and did not pop a switch. (4) Hooked up the low voltage wiring and the system was in standby with the fuse not popping. Thermostat was still blank. (5) Found no batteries in the thermostat. Added batteries and the display worked. The client stated that he replaced it about a day prior. (6) The fuse most likely popped when he was replacing the thermostat. (7) Ran system for 5 minutes in heating. The fuse never popped and all heating switches were working properly. The inducer motor will need to be replaced sooner rather than later, however. (8) System is operational upon departure.