why does my delonghi blow the house electrics after 20 mins cooking time?

From what you have said it appears that your cooker is tripping the RCD which protects your house.
To briefly explain how a RCD works.....RCD stands for residual current device and it will detect if there is any electricity leakage to earth.If it detects a leakage...however small it will cut out as it has detected a fault.
If your cooker is only tripping the RCD when the fan is on then i would bet that the fan motor is faulty. I would replace the fan motor .
Hope this assists.

Paul
August 2007