I started out with eggs on the top shelf and the middle shelf (altered by attaching PVC legs to make it 1" lower then the lowest shelf setting), water bowl on floor. This worked well with the heat set on 99* from when I set eggs at 8:30am untill about an hour before my post about problems.
I then rearranged the setup thinking that was the issue...
I then lowered the top shelf to the middle shelf setting, placed the other tray of eggs on the floor and placed the water in on the middle shelf. I right now have the water out. I am still getting about a 10* difference from top to bottom. I mean it was fine, I opened to turn, and then it just went a little crazy. The only ones I can fit in right now are stick style or only read right now temps.
what do you have the heat set on now?
thermometers will spike as the incubator heats and cools because they are reading the immediate air temperature... it's the overall temperature that matters..
even in homemade bators the air temp will fluctuate a bit as the heating element comes on... so long as the overall temp inside the eggs stays constant.. they will be fine...
if the readout on the incubator is set at 99... it won't heat to 103.. it should shut off at 99.... does the display continue to rise over what you have it set at? If it does.. is the incubator sitting next to a window where the sunlight is shining on it?
The readout on mine is set for 100... there have been a few times when I moved hot eggs from another bator into mine where the temp would flash at 101 for a few seconds.. but that was because it was registering the temp of the heat rising off of the eggs.. it wasn't still heating
You said you are getting a 10 degree difference between the top and bottom... in mine I get a 1 degree difference between the top shelf and lowest shelf setting... maybe try trading the top thermometer for the bottom one.. I am suspecting one of them may be a bit off if they are showing a 10 degree difference
for mine.. the display is set to 100
the top shelf is reading 99.5
the bottom shelf is reading 98.5
I don't have a reading for the bottom simply because I am not incubating down that low with eggs right now.. that si the area where I add a water tray if I need to raise humidity