there are many reasons for a control to lockout first i would forget warrenti on the control it seems they are guessing and if you cant fix it replace it seems to be the way they work. we are at a major disavantage on this one hard to say what it is without being there. robershaw did have problems with thier control at one time but they resolve the problem a few years ago so chances are you didnt get one with the problem. i am about to go against something i said in an earlyer post on an other page hehehehe. look for a nate cirtified co with a nate heat tech. this should not be to hard to resolve if the tech has the correct tools. change that milivolt stat first