Can I Kasher my oven for Pesach or during the year with a blow torch?
A oven can be Kashered with a blowtorch. However, using a blowtorch on the inside walls of a oven until it is red hot (what would be required if using that method) can be very dangerous and would ruin the oven. The fact that it is dangerous and can ruin the oven is also a reason why the Kashering should not be valid according to Halacha, as there is a concern that one might not do a proper job.
Additionally, it is very likely to miss a spot causing the oven not to be Kashered.
Therefore, unless it is done by a professional in this field that would insure that it is done properly, the following methods should be used:
Self-cleaning ovens: if the oven has a self-clean setting (a “continuous cleaning” setting is not the same), the metal cover separating the actual fire from the oven cavity (where you place the food) should be removed. The self-clean cycle would suffice provided a complete cycle has run. If your oven has a glass window it should be fully covered.
Non self clean ovens: The grates must be blow torched by a professional till they are red hot. The oven should then be switched on for an hour on the highest setting. After this, one may bake food only if double wrapped or in an insert.
ראה שוע”ר תנא, ט-שמא יחוס וכו’ וה”ה כאן.