If it's doing it every 5 minutes it sounds like the temperature is dropping too fast or there isn't a large enough gap between the temp you want it at and the temp you want it to turn on(make sense?). If you want a temp threshold.

I would try a couple things:

1. Read the manual and see if you can set it to turn on at a specific temperature. Like mine is set to 100 but clicks on at 95. Size of heat pad may make a difference in as well.

2. Possibly insulate it with foil tape. I've found foil tape helps make the hot spot a little larger and keeps the heat from dissipating into the air.