I would expect you do need an electrician.
1) Normally an oven would have a dedicated supply.
2) If the "Switch" you refer to is a MCB then something may have burnt out in the oven.
3) If the "Switch" you refer to is a RCD then may be your oven is only damp and needs drying out.
It is not normal in past years to connect ovens and cookers to RCD's because of the problems with damp but where the "Cooker Switch" has a 13 amp socket incorporated some electricians would connect it to the RCD side. Under the new regulations from July 1st then I would expect it would be feed from it's own dedicated RCBO which is a MCB and RCD combined.
An MCB protects against an item using too much current and in the case of a built in oven would be selected according to the oven manufactures recommendations somewhere between 10 and 45 amp and unless a local fuse is fitted will only run the oven. Kitchen fitters often did not follow these simple rules and would connect to what ever is handy.
Heating elements in ovens can't be fully sealed because of the heat and have mineral insulation this will absorb moisture and if the oven is not used for some time can result in the RCD which measures earth faults normally rated at 30ma to earth to trip. Normal cure is to use a temporary supply with the room empty to dry out the oven and then re-correct to RCD supply once dry. To work out which one is your problem and cure it really needs an electrician on site.
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