Aslong as you prove that it's definitely off you will be ok, the easiest way to this without a meter is:
1. Switch the cooker on then knock off the relevant circuit breaker check the cooker is off.
2. Then switch the circuit breaker on again and check the cooker comes back on.
3. Again knock the circuit breaker off.
You will now know you are isolating the right circuit, there's been quite a few people who have came unstuck by going off the labels on the front of the circuit board, they aren't always right !!!