Question: If a kettle stops working because of an electrical fault, and it is repaired by a non-Jew, does it require tevila?
Answer: The Shulchan Aruch (Yoreh De’ah Siman 120 Se’if 10) discusses a situation where a non-Jew creates a utensil with materials that are owned by a Jew, and rules that the utensil does not require tevila. The Remo (ibid) quotes opinions that obligate the utensil in tevilas keilim, and the Remo writes that the utensil should be immersed without a brocho.
Therefore, in your situation where the kettle is repaired by a non-Jew, the most ideal would be to immerse the kettle, but without a brocho.