72 Pa. Stat. § 5452.13a
Whenever, through mathematical or clerical error, an assessment is made more than it should have been and taxes are paid on such incorrect assessment, the Board of Property Assessment, Appeals and Review, upon discovery of such error and correction of the assessment, shall so inform the appropriate taxing district or districts, which shall make a refund to the taxpayer or taxpayers for the period of the error or six years, whichever is less, from the date of application for refund or discovery of such error by the board. For the purposes of this section, in counties of the second class, "mathematical or clerical error" shall mean the difference between the assessment as certified for a given tax year by the Board of Property Assessment, Appeals and Review and the assessment upon which taxes are billed and paid. Reassessment, revision of assessment or certification of assessment with or without application by the owner as a decision of judgment based upon the method of assessment by the board shall not constitute an error under this section.
72 P.S. § 5452.13a