Kanchigai no Atelier Meister - Eiyuu Party no Moto Zatsuyougakari ga, Jitsu wa Sentou Igai ga SSS Rank Datta to Iu Yoku Aru Hanashi

the unaware atelier meister - One day, Kurt, a kind-hearted boy, is suddenly kicked out of the Hero's Party for being "useless". He finds that his aptitude for weapons, magic, and all other combat-related skills is the lowest rank, so he takes odd-jobs repairing the castle walls and digging for minerals to make a living, where his exceptional abilities are immediately revealed. He proves to be skillful in cooking, building, mining, crafting magical tools--in fact, his aptitude for every skill unrelated to combat had an SSS-ranking! Kurt, however, seems completely unaware to his talent and ends up saving people, the town, and even the country through his unaware actions!?

(Source: Alpha Manga)