AEG Competence B2100-1 built in oven

I have an AEG Competence B2100-1 built in oven. It is about 18 months old and it has developed an intermittant fault. With the power switched on, the “Oven Power Indicator” lights and the clock appears to be displaying normally but none of the oven functions work. The oven light, the grill, the fan, the oven itself, none of them work. The temperature pilot light doesn’t glow. I’ve tried resetting the clock and the clock functions. I’ve tried switching it off for 15 minutes but it still doesn’t work. Then out of the blue it works again. At the moment this is happening about once a week. It’s normally working again within about 30 / 40 minutes. Any suggestions?