Our Bauknecht gas hob ignition, keeps going off on its own?

Hi

We have a Bauknecht gas hob & electric cooker.
Please please can you help us our hob ignition keeps going off
sometimes we can play around with the button and it stops or put something heavy onto it and it stops, but it goes off all the time and it is driving us mad, We can stop it, and then for no reason it goes off, it can be any time of the day or night.
Any suggestions will be really helpful

Thanks

Jo. A
January 2007