When no hot water can justify leaving
Possibly, but be careful. If a long-term loss of hot water makes a rental unlivable and the landlord will not fix it, California law may allow you to move out under "constructive eviction" — but doing it the wrong way can leave you owing rent.
Breaking a lease is a serious step. Constructive eviction generally requires severe conditions, notice to the landlord and a fair chance to fix them, and that you actually move out because the home is unlivable. A brief hot-water outage usually will not qualify, while an extended failure the landlord refuses to address might.
Because the risk is real, run this past an attorney before you act. Before you move out over no hot water — or sign anything the landlord offers — a free, confidential review can help you avoid a costly mistake.
This is general information about California tenant rights, not legal advice. Every situation is different.