My Whirlpool double oven will not maintain the set temp. I replaced the control panel about a year ago when everything went blank and it had worked fine till about 2 weeks ago. I placed an oven thermometer in the oven, set it to 350 and noticed it was going as high as 400 and then back to 250 before turning back on. I then replaced the oven temperature sensor and tried it again. Now it keeps it above 350 and sometimes will go as high as 425. Any suggestions on what it might be? Is the control panel the problem again?