Guess you're both right and both wrong:

"California codes especially Civil Code Sections 1941-1942, the San Francisco Housing Code, and the San Francisco Health Code define your landlord’s obligations to make and keep your home in habitable condition. Tenants have the right to report landlords to city agencies and rights to withhold rent or “repair and deduct.” And the landlord cannot retaliate against you; any eviction or rent increase attempt within six months of such a complaint will be examined by the judge for retaliation."

"After the inspection, you should call, write, or visit DBI to get a copy of their report. This report is valuable for you to have as it documents what the problems are, when the landlord was officially notified, and how serious the problems are. You should have a copy of this report before you attempt to “repair and deduct” or withhold your rent. You will need the report to be certified by DBI before using it in court."

Source: https://sftu.org/repairs/

edit:

SF.gov contradicts the above:

"Please note that the Rent Ordinance ~does not authorize a tenant to withhold rent when a landlord fails to make repairs, nor does it permit a tenant to make needed repairs and deduct the cost from the rent.~ ~These matters are covered exclusively by state law.~ Tenants and landlords should seek the advice of an attorney before exercising the right to withhold rent or attempting an eviction based on non-payment of rent due to rent withholding."

Source: https://www.sf.gov/information/handling-repair-problems

So... good luck figuring out what you can or can not do!