There is no hard and fast rule for this.That said, a good rule of thumb would be to provide at least two written notices, sent someway you can prove delivery (e.g. certified mail, with return receipt; fed ex; fax with confirmation report) and--very important--a "reasonable time" after each notice (maybe 2 - 4 weeks) to address, or at least schedule to address, the problem.Note you may NOT withhold rent to force the landlord to repair. What you may do is make the repairs yourself and deduct the actual cost of the repair; furtheremore, you can only generally do this for conditions affecting habitability or safety (so, for example, for water leaks, lack of water or heat, broken windows or door locks...but not for a sticking kitchen cabinet, one burner out of four being out on a stove, etc.).