How warm the heat must be able to make your home
California requires rentals to have working heating facilities, and many local codes set a minimum indoor temperature the landlord's heat must be able to reach — often around 68°F during daytime hours, though it varies by city.
The exact number and the hours it applies can depend on local code, but the basic idea is that the heating system must actually be able to warm the home to a livable temperature. A heater that runs but cannot get the unit reasonably warm may not meet the standard, especially when the cause is a failing system the landlord has not repaired.
If your heat cannot bring the home to a livable temperature, note that when you report it, since it is a real habitability concern rather than a preference. If your heat cannot keep your home reasonably warm and your landlord will not fix it, a free review can help you understand your options.
This is general information about California tenant rights, not legal advice. Every situation is different.