Apparatus and methods for treating skin conditions that deliver high frequency energy to a patient's tissue. The apparatus has a treatment tip configured to be removably coupled with a handpiece and a conduit inside the handpiece. The treatment tip includes an electrode configured to deliver the high frequency energy to a region of the tissue, a channel for circulating heat transfer fluid proximate to the electrode, and an inlet passage to the channel. The conduit includes a tubular sidewall with a lumen used to transfer the heat transfer fluid from the handpiece to the inlet passage of the treatment tip. When the treatment tip is coupled to the handpiece, a septum covering the inlet passage is configured to be pierced by the conduit to define an opening for coupling the conduit with the inlet passage. When the treatment tip is removed from the handpiece, the septum substantially seals the opening.