Came across this problem at weekend brandnew range installed 40amp mcb on RCD side of split load board. Cooker isolator is 2 gang with socket out let. The rcd trips when ovens are on I know the reasons but was wandering how you go on with regs as all i could do was move mcb over to none rcd side of board so now you have a socket in a kitchen thats not got rcd protection do I
1. change cooker isolator to one gang without socket, don't think owner would be too happy as it would require backbox to be moved and some more tiling.
2. label socket outlet warning notice etc
3. Become a joiner!!!
Sounds like a faulty element, if all is ok when power is on the oven but nothing is switched on but soon as switch on the oven and the element heats ups the it is going to earth as insulation is breaking down thus causing element to trip RCD. When you test it later when cool it will seem as if the is no problem.
You will need to be there when oven is switched on and when it trips the RCD you will need to give it an insulation test straight away before it has time to cool down and fault dissappears.