I had the same luck with mine. It was my first incubater I got it a couple years ago. First 2 batches were great. Then, I would be lucky if I got 2 to hatch out of 20! Numerous failed hatches and dead chicks! Always eggtopsied and had dead nicely developed chicks. After searching here...I found that heat spikes and temps are apparently a common issue. I plugged it in a few days ago because my purchased eggs are due today. I followed the directions here to test thermometer with ice water. It read up and down around 50 degrees! I put my finger on the ice thinking maybe, somehow it wasn't in well. THE DARN THING SHOCKED ME!! Never again will I trust one of these.
I have located a Hovabator at a store over an hour away...I am making the trip to get it and all it's accessories!