I have this as a double oven. The top one is a convection oven. The bottom is just a regular one. Today I went to cook something in the lower oven and set the temperature to 350. It indicated Lo and underneath, the note saying "pre heat". It has stayed there for 1 hour? I have never seen this before. Usually it says Lo and then the temperature as it comes to the desired temperature. I have cancelled and repeated with the same result. Any suggestions as to what is wrong? The top oven is working fine.