(a) Except as provided by this section, the tenant has the burden of proof in a judicial action to enforce a right resulting from the landlord's failure to repair or remedy a condition under Section 92.052.
(b) If the landlord does not provide a written explanation for delay in performing a duty to repair or remedy on or before the fifth day after receiving from the tenant a written demand for an explanation, the landlord has the burden of proving that he made a diligent effort to repair and that a reasonable time for repair did not elapse.
Official text of the Texas Property Code as published by the Texas Legislative Council.