Repair vs. replacement timelines
When a broken water heater leaves you without hot water, the landlord must repair or replace it within a reasonable time — usually promptly, since hot water is a basic requirement. A simple fix should happen fast; a full replacement may take a little longer.
A minor repair, like relighting a pilot or swapping a part, should be handled quickly. If the water heater has to be replaced, that can take somewhat more time to arrange, but the landlord is still expected to act without unreasonable delay and to keep you informed of the timeline.
Long, unexplained delays that leave you without hot water can become a habitability problem, no matter the cause. Report the issue in writing, note when it started, and follow up if you hear nothing. If your landlord will not repair or replace a failed water heater promptly, a free review can help.
This is general information about California tenant rights, not legal advice. Every situation is different.