In this project the focus has been on the system for recombination at Oskarshamn 2. The recombining systems have on several occasions switched paths due to low pressure before the last ejector that’s feeding the recombiner. Of the mentioned reason, events and several measuring points have been analyzed in this report since the installation of the recombining systems. In order to prove theories and demonstrate what may be the cause of this problem, we used heat balance calculations by the program Probera. Using the program, we can demonstrate that the catalytic process does not reach the desired temperature with the amount of combustible substance. We have used Oskarshamn 2's simulator to see what happens at increased concentration of hydrogen in the recombiner. The project demonstrates how the controlsystem can be changed for a greater margin to switching paths and thus should provide a more stable process. Analysis shows that setpoint have been reached extremely rarely. Even regulator gain and integration time proved to be incorrect when the system falls intoself-oscillation.