We have model # 153-7758. For years we'd always had it displayed and working in farenheit. But we accidentally did something to it last year and now it displays, and works in celsius! So if we have it on 23 degrees celsius, we are too cold. But moving it just one notch up to 24 degrees celsius we are much too hot and can't sleep. How can we change mode back to farenheit? We have tried everything we can see on the instructions!