Spike recommends not plugging in both the heating and cooling at the same time because you will have them working against each other and running more often. If your room is warmer than your target temp, just plug in the cooling, and vice versa.
Mine only ever overshoots cooling by maybe 1.5 degrees F, and I just let it naturally and slowly warm back up until it triggers the glycol pump again.
One tip I would have is don’t ever unhook your glycol lines from the fermenter lid and leave them unattached (even if the pump is unplugged). I unhooked my lines and unplugged the pump when it was time to clean after I completed my first fermentation in my Spike CF5. I made sure to leave the open ends of the tubes laying above the level of the chiller so that nothing would flow out due to gravity.
Well later I decided to drop the temp on my chiller a couple of degrees, and I guess the temp drop caused a pressure change that resulted in about half of my glycol flowing out of the tubes all over my floor. That was fun. So if you unhook those lines from the coil lid, make sure you don’t leave them unhooked for long.