Oven will heat up, but then will not maintain desired temperature.

Both gas and electric ovens will cycle on and off throughout the cooking cycle to maintain the set temperature. When the oven temperature has dropped below the set temperature, the oven cycles on again to provide heat and will cycle off again once the temperature is higher than the set temperature.

Hello, Cristina -

Since you have not stated the make and model of your oven, all I can advise is for you to turn your oven on and set it to the desired temperature and wait for 10 - 15 minutes until the oven comes up to the full heat temperature.

You can read the instructions here, if you wish:
https://www.wikihow.com/Preheat-an-Oven

Best wishes.

if it is an electronic timer temp controller you might want to check it

I GOT THE SAME QUESTION .. IT IS A GAS OVEN . WHEN THERMOSTAT IS SET TO GAS MARK 4 WHICH IS EQUIVALENT TO 350 DEGREES , AFTER 10 MINUTES, IT REACHES ITS DESIRED TEMP. BUT IF I DON'T ADJUST THE FLAME, THE TEMP WILL RISE HIGHER AND HOTTER THAT I NEED TO OPEN THE OVEN DOOR TO DECREASE THE TEMPERATURE INSIDE. ANYONE KNOWS IF THAT IS NORMAL? THANKS

t stat

sounds like it needs a new temp thermistate

This sounds like a weak igniter, it would have to be a gas oven and the symtoms usually are: takes longer than normal to ignite the burner, may or may not smell gas in the oven, does not maintain set temperature, eventually won't heat at all. On gas ovens, a glo igniter is like a light bulb, the more you cook, the faster it wears out. Bottom line, needs to be replaced. Good luck.

replace the thermostat temperature probe inside the oven, that is the cause of this problem alamost 100% of the time

After it drops temperature, how do you get it back to the desired degrees? It sounds like the thermostat isn't keeping up.