Hello,
If you would like to diagnose it yourself, and you own, and know how to work a multimeter, as well as know the dangers of working with electricity please proceed:
This oven is easy to diagnose, especially if only one of the elements is not heating.
1) You'll need to slide the oven out about 10" to be able to remove the access panel at the top.
2) Once the panel is removed you'll see two relay boards - one on the left and one on the right. The left side board has the relays which control the upper oven elements.
3) On the left side relay you'll need to locate a single spade terminal labeled, "Broil 2" which has wire number 43 on it. This is where one side of the conv. element gets 120vac. With the unit turned off, remove that wire.
4) To the right of that wire and towards the center a little bit you'll find a single spade with 3 wires on it. This terminal will be labeled "DLB". This is where the other side of the element gets it the second leg of 120vac.
5) At this point you can check for power or ohm out the element. If you would like to ohm it out, it should measure 18 ohms. If you would like to check for power, while in Convection Bake, each of the terminals that the wires were removed from should measure 120vac between the terminal and chassis or neutral.
6) If you find there's an open when touching the wires you'll need an element, part number 484787. If you find no voltage on the board you'll need it, # 492071.
If this seems a bit too much for you you can also pull the convection baffle off, remove the element and ohm the element out from there, as well as check for power on the wires. If you decide to go this route, make sure the wire's don't slip back into the insulation.
Good Luck.. | 
