72 Pa. Stat. § 5860.311
On the first day of January next following the notice hereinbefore prescribed, if the amount of the tax claim referred to in the notice has not been paid, or no exceptions thereto filed, the claim shall become absolute. Every such claim shall bear interest as hereinbefore provided to the date of payment, or date of sale held under the provisions of this act, except in the case of claims where the owner is paying his taxes under the provisions of any law abating penalties, interests and costs, or either, in which case the claim shall bear no interest and costs, unless there is a default in payment, in which case interest shall run on the amount due on the claim at the time of default, and penalties, interest and costs abated shall be added as provided by the act of Assembly abating the same.
72 P.S. § 5860.311