Upon arrival unit was on but was not running. Went tot the thermostat and there was a call for heat and the fan was in the on position but the furnace was not running. Checked power from the thermostat to the zone board and had a call for heat. Checked at the furnace control board and had a call for heat. Upon further investigation we found the fuse on the furnace control board had popped. Checked all wiring from the furnace board to the control board and found a loose wire connection. Tightened the connection and replaced the furnace fuse. Turned power on and the furnace started up right away. Watched the furnace cycle on and off. Unit is working properly.