Answer: A landlord has a legal duty to make appropriate repairs and to do so promptly once notified.
The rules governing landlord entry into a rental unit are stated in California Civil Code Section 1954. This statute says that a landlord may enter only during normal business hours and only for a legitimate reason, which includes repairs, and only after giving 24 hours written notice to the tenant.
Once the landlord complies with these requirements, he can enter the rental regardless of whether you are present. A tenant does not have a right under this statute to insist on being present, nor can a landlord require the tenant's presence.
A landlord should have a key that enables him to enter the unit and let contractors in for repairs. In addition, the landlord has a duty to protect your property from damage or theft whenever entering the rental unit, regardless of whether you are present.
Of course, you and your property manager are free to negotiate an agreement to allow the plumber to enter your unit. Hopefully you can find an alternative that works for both sides.
Eichner is director of Housing Counseling Programs for Project Sentinel, a nonprofit agency providing tenant-landlord and fair housing counseling in four Bay Area counties. To submit a question, contact firstname.lastname@example.org.