Complete 1 system furnace repair and preventative maintenance check. Fan would not turn off after the customer changed the thermostat. The screw had damaged thermostat wire. Added electrical tape to wires to prevent them from shorting out. Tested mechanical and electrical components. Found weak flame safety sensor. Recommend repair. System has no overflow protection switch, recommend adding on to protect furnace from potential water damage and to serve as a backup to primary water safety. Furnace has no surge protection, recommend adding on to protect furnace from power surges. System is heating at this time.