The Be’ur Halacha (Rav Yisrael Meir Kagan of Radin, 1839-1933), in Siman 548, writes that as a general rule, one may not hire Jewish workers to do professional work on Hol Ha’mo’ed. One exception to this rule is work that is necessary for the purpose of Ochel Nefesh – food preparation. One may hire Jews to perform such work on Hol Ha’mo’ed, and pay them for their services, even if professional work is needed. The Be’ur Halacha adds, however, that if somebody is willing to perform the service for free, he should be brought to do the job.
Hacham Ovadia Yosef, in Hazon Ovadia (p. 186), applies this Halacha to kitchen appliances. If one’s refrigerator, freezer, oven or stovetop requires repairs, one may hire a Jewish worker to do the work, and pay him for his services. If there is somebody available willing to do the repairs for free (which is not very common), one should have this person do the work, but otherwise, one may hire a professional and pay him for his service, since all these appliances are necessary for preparing and storing food for the holiday. This also applies to other appliances needed for food preparations, such as a mixer or blender, as well as the kitchen faucet, which is likewise needed when preparing food.
Summary: Although generally one may not hire a Jew for professional labor during Hol Ha’mo’ed, one may hire a Jew to repair kitchen appliances – such as the refrigerator and oven – as they are needed for the preparation of food.