My oven won't reach temperature all the time. it

Question edited for clarity and make some sentences.
Question moved form Misc.

It sounds like you have a bad temperature sensor. Some can be calibrated, but not by a hundred degrees.

https://www.google.com/search?q=ge+jb250df1ww+calibrate+oven+temperature

The temperature for the TCO in your fan oven should be set to the desired cooking temperature for your recipe. This will depend on the type of food you are cooking and the recipe you are following.

For example, if you are baking bread, a typical temperature would be between 350-450 degrees Fahrenheit. If you are roasting a chicken, a common temperature is 375-400 degrees Fahrenheit. If you are cooking a casserole, a good starting point is 350 degrees Fahrenheit.

It's important to follow the recipe or guidelines for the specific type of food you are cooking, as the correct temperature and cooking time will vary based on the ingredients and method

that would be normal. if it didnt shut off, it would go above the set temperature. the heat is either off or on. it cant me in the middle. it turns 'off' so that the temperature doesnt go too far above 250. when it senses the temperature falling too low below 250, it heats it up again.

Google GE electric oven Model number: ? Manual

either its the oven sensor rod located at the top of the ovens cavity,or your bake element could be getting a hot spot which is when it gets a discolored spot in the element and can no longer pass sufficient current to heat the oven past 250 degrees

It could be either . The sensor can be checked with a good meter room temp should be around 1200ohms and change with added temp.

Your oven temperature sensor is bad replace it.
Part # is 7430P008-60

meter the electric-220 metering the positives...110 metering 1 positive & ground at a time...Ohm the element if shows open(10 dollar multimeter doesn't move) then is bad.Can be reached from the back just above where the power attaches,for safety disconect the power

Page 6 of the owner's manual:
Adjust the temperature calibration.