FGET3069UFA Frigidaire Wall Oven - Overview

When I start the oven it comes up to temperature but will drop anywhere from 50-75 degrees and won’t keep the temp steady. I frequently have to doublecheck the temp by resetting it to some other temperature and then the oven will preheat and at that time the over self reports the actual temp which is anywhere between 50-75 degrees cooler than what I originally set the temp. For example, I am baking something at 350, I will set the oven temp to 350, the ovens, either top or bottom comes up to temperature and notifies me, I then put my food in the oven and start baking. I come back 20 minutes later and the oven temperature is about 50 degrees cooler. I set the temp to 375 and the oven then tells me the actual temperature is 305 or 310. It seems that once it comes up to temperature it just starts cooling down. My oven is a Frigidaire model FGET3069UFA.