When I set to temp on bake the oven only heats up to 25 below the desired temp in the top oven. Intermittently, it will not hold that temp either & the fan ran about an hour and half last night. The broiler heats up, the element turns red and the mother board says it's 550, but an in oven thermometer says its 500. We replaced the temp sensor about a year ago and we think the oven is about 15 years old.

The bottom oven appears to be functioning just fine.

Thanks for any guidance.