cannon culinaire goes off

Hi I have a cannon culinaire built in double oven, few years old now (cannot find model number on it) problem is intermittent cuts out whether on the bottom oven or the top one. the gas goes off the oven light goes off but the exhaust fan still runs. It is more common after about ten minutes after switch on and sometimes just re- ignites itself but usually have to turn off/on several times before it fires up again. Anybody any ideas of the possibilities.
cheers