What part needs to be replaced when broil comes on with every oven setting? For example, I set the oven to bake at 350. The bottom element comes on for bake, but the broil also comes on. The panel registers the 350 degree bake setting, but the broil element stays on bringing the oven up to over 500 degrees and it stays on. What part needs to be replaced? Is it worth fixing for an oven over 5 years old? Thank you in advance.