An on-demand, closed-loop fluid heating system with a control system for providing fluid on-demand at consistent desired precise temperatures. A device for sealing a cervical opening includes a support structure, and a member coupled to the support structure, wherein the member is inflatable to create a seal for abutting against cervical tissue. 0 \u03bcm or less, and the glass frit is glass frit that has an average particle diameter of 5 \u03bcm or less and does not contain lead such as borosilicate glass. The optimal time interval over which the battery pack should be warmed is a function of the operating mode and the previously calculated temperature difference.