I have a fairly new furnace. It runs good heat. After the furnace stops running the fan/blower runs as usual. But lately it's been turning on and off. The fan will turn on as usual then about a minute later it will turn on for approximately 30 seconds, turn off for one or two minutes, then back on for 30 seconds. It will do this 3 or 4 times until it finally stops. It's an automatic fan switch. It's a beckitt furnace. My boyfriend is handy but neeed some advice. Thanks!