Smeg A2A-5?

My son has a Smeg A2A-5 range cooker purchased from a kitchen supplier two years ago as a X display but he is unable set and leave the clock as the cooker has to be switched off because the main oven light is permanently on, is this something done in the showroom as a display function and if so can I fix it with an adjustment or will it require a part change? I am an electrical engineer and I have over 40 years of fault finding experience but I would like to find out some information before I start looking