No working heat on day one
A landlord must provide a livable home from the start, so no working heat at move-in is the landlord's responsibility to fix right away — and a unit that cannot be heated may not have been fit to rent.
Working heat is a basic requirement, so it should function when you move in, not something you discover missing on a cold night. Report it to your landlord immediately and in writing, and document that it was not working from the start with dated notes, temperature readings, or video.
If a landlord rented you a unit knowing the heat did not work, that raises concerns beyond an ordinary repair, since landlords are not supposed to offer a home that fails the basic standard. Keep your move-in paperwork and early communications. If you moved into an apartment with no heat, a free, confidential review can help you understand your rights.
This is general information about California tenant rights, not legal advice. Every situation is different.