A medical treatment system, such as peritoneal dialysis system, may include control and other features to enhance patient comfort and ease of use. For example, a peritoneal dialysis system may include a control system that can adjust the volume of fluid infused into the peritoneal cavity to prevent the intraperitoneal fluid volume from exceeding a pre-determined amount. The control system can adjust by adding one or more therapy cycles, allowing for fill volumes during each cycle to be reduced. The control system may continue to allow the fluid to drain from the peritoneal cavity as completely as possible before starting the next therapy cycle. The control system may also adjust the dwell time of fluid within the peritoneal cavity during therapy cycles in order to complete a therapy within a scheduled time period. The cycler may also be configured to have a heater control system that monitors both the temperature of a heating tray and the temperature of a bag of dialysis fluid in order to bring the temperature of the dialysis fluid rapidly to a specified temperature, with minimal temperature overshoot.