How quickly heat must be restored
A landlord must restore heat within a reasonable time after being notified, and because heat is essential — especially in cold weather — that usually means quickly, often within a day or a few days, not weeks.
There is no exact deadline in the law, but "reasonable" shrinks dramatically for heat during cold weather. A short delay to make a repair may be understandable, while days or weeks without heat in winter — particularly after you reported it — generally is not. The stakes are higher for infants, older adults, and anyone with medical needs.
Report the problem in writing and keep track of how long you have gone without heat, since that record matters if the landlord drags things out. If your landlord is stretching a heat repair well past a reasonable time, especially during cold weather, a free review can help you understand your options.
This is general information about California tenant rights, not legal advice. Every situation is different.