Zanussi doouble oven tripping rcd when no elements are on

I have a Zanussi zbs 703 A oven and it is tripping the RCD in the consumer unit when any of the right hand side grill or oven (fan oven, upper oven and lower oven) are selected when the temperature dial is set to 0.

Also the fault seems to have “transferred” itself from the left hand side oven to the right hand one!

I am guessing it could be a fault that is common to heater ccts?

At first the oven may be used for a few minutes until fault happens, then the RCD trips immediately each time the right hand side grill or oven is selected.