my AEG Competence B4100-1 cutting out after about approx 15min?

I have a competence B4100-1 under oven.the oven switches on ok and goes on and off with the thermostat,but after about 15-20 mins it cut out and every thing stops.then a while after it has cooled down you can turn it on again and the cycle of events starts again.Also there is no label with a serial number for model reference near the door or anywhere else on the oven,I suspect it has come off when being cleaned,which is making it difficult to reference the part, as I get asked for this number so that the supplier can identify the correct part .Can anyone help with advise on this problem