If the landlord won't fix a serious habitability problem after proper notice, you may have options: 'repair and deduct' (fix it and subtract the cost, up to one month's rent, max twice a year), withholding rent, or reporting to a code inspector. Use these carefully — they have strict rules.
Under Civil Code §1942, after giving the landlord reasonable notice and time to fix a habitability defect, a tenant may pay to repair it and deduct the cost from rent — limited to one month's rent and usable no more than twice in any 12-month period. Other remedies include withholding rent (risky — best done with legal guidance and only for serious defects), suing for damages, or contacting the local building/code-enforcement office. Retaliation by the landlord for exercising these rights is illegal (Civil Code §1942.5). Because misusing these remedies can lead to eviction, tenants should document the problem, the notice given, and consider legal advice before acting.
SerenityLease provides general legal information, not legal advice. Consult a licensed attorney for situation-specific guidance.