OK I don't get it I have no problems at all with my LGs. You said the temp was stable before you set the eggs. Did you touch the knob after you set the eggs? Here is how to properly set up a LG. Put bottles of water or pint containers of sand in LG. Start increasing the temp a little at a time to bring it up to 102F at the top of the egg, or 98F at the bottom. Use plastic eggs or just some eggs for eating, you can still eat them after. Make sure you calibrate your thermometer first. What you are looking for is a temp of 100F in the middle of the egg for a still air. Now this is the temp at the warmest part of the day. This process will take a few days, NOT hours. The bottle of water is to stabilize the bator as if it has eggs. Once you reach a temp of 100F at warmest part of day leave it alone for a couple days before setting eggs. Once it holds do NOT ever touch the knob to increase the temp, even when the temps drop. Set eggs and leave alone for first 24 hours. Now when the bator temp drops from setting the eggs leave it alone. When you start to turn the eggs and the temp drops leave the stat alone. ONLY adjust temp in down direction if temp goes over 102 this is common for eggs to throw of heat as the chicks begin to move in shell. The temps will drop every night the same as they do under a hen. Leave the temp knob alone. As mentioned before put a dimmer switch knob and mark a indicator line on knob. When you do have to adjust down on temps mark where it originally was and do not go above it.
Now if you are only setting a small number of eggs add bottles of water or pint containers of sand to absorb up and down temps. This also helps with opening the bator to turn eggs. Put sponge pieces on top of sand and add water for humidity as needed. Did I mention leave the temp knob ALONE.
If this is too complicated then spend hundreds or thousands of dollars on expensive incubators. Or buy one of the digital thermostats for reptiles I believe they are around 30 to 50 bucks USD.
Now if you are only setting a small number of eggs add bottles of water or pint containers of sand to absorb up and down temps. This also helps with opening the bator to turn eggs. Put sponge pieces on top of sand and add water for humidity as needed. Did I mention leave the temp knob ALONE.
If this is too complicated then spend hundreds or thousands of dollars on expensive incubators. Or buy one of the digital thermostats for reptiles I believe they are around 30 to 50 bucks USD.