Thermostat wont connect to furnace?

honeywell programmable thermostat has a fan on option but will not turn on the blower. Circuit breakers are on. Wiring has been checked. Everything was working, then there was a gas service (to properly cap off some unused lines), and the thermostat was moved (but wiring is fine). Now there seems to be no connection between the thermostat and the Carrier 8000. The thermostat has new batteries and power. If the gas supply was not turned back on, wouldn't the fan on still work? What else can I check to see why there is no control?