Very probably the heating element has developed a fault - as the wire inside it warms and expands it touches the outer case and that causes an earth leakage trip - all the electric goes off.
The wire cools down and shrinks and no longer touches the outer case and off you can go again.
A service engineer will be able to replace the element.
There are videos on Youtube (mostly American) that show how to change an element.
Good Luck...
May 2017
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