What industry does maintenance belong to?

Service industry. Maintenance includes boiler maintenance, maintenance and repair, as well as technical support, consulting services and other technical services in the field of application services, belonging to the industrial technical service industry. Service industry is the general name of industries in the electronic information age, which refers to the business of providing services to the society by using equipment, tools, places, information or skills, including agency, hotel, catering, tourism, warehousing, leasing, advertising and other services.